diff --git a/packages/editor/package.json b/packages/editor/package.json
index 817a2ae8c..fc6600992 100644
--- a/packages/editor/package.json
+++ b/packages/editor/package.json
@@ -91,6 +91,7 @@
     "@portabletext/patches": "workspace:^",
     "@portabletext/schema": "workspace:^",
     "@portabletext/to-html": "^5.0.2",
+    "@sanity/json-match": "^1.0.5",
     "@xstate/react": "^6.1.0",
     "debug": "^4.4.3",
     "scroll-into-view-if-needed": "^3.1.0",
diff --git a/packages/editor/src/behaviors/behavior.abstract.insert.ts b/packages/editor/src/behaviors/behavior.abstract.insert.ts
index c38a06cf2..840c86826 100644
--- a/packages/editor/src/behaviors/behavior.abstract.insert.ts
+++ b/packages/editor/src/behaviors/behavior.abstract.insert.ts
@@ -1,4 +1,5 @@
 import {isTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import {isSelectionExpanded} from '../selectors'
 import {getFocusInlineObject} from '../selectors/selector.get-focus-inline-object'
@@ -21,7 +22,7 @@ function getUniqueBlockKey(
       return snapshot.context.keyGenerator()
     }
 
-    if (snapshot.blockIndexMap.has(blockKey)) {
+    if (getIndexForKey(snapshot.context.value, blockKey) !== undefined) {
       return snapshot.context.keyGenerator()
     }
 
diff --git a/packages/editor/src/editor/Editable.tsx b/packages/editor/src/editor/Editable.tsx
index d2fa74b8f..7065c979b 100644
--- a/packages/editor/src/editor/Editable.tsx
+++ b/packages/editor/src/editor/Editable.tsx
@@ -247,7 +247,6 @@ export const PortableTextEditable = forwardRef<
             value: slateEditor.children as Array<PortableTextBlock>,
             selection: normalizedSelection,
           },
-          blockIndexMap: slateEditor.blockIndexMap,
         })
         if (slateRange) {
           slateEditor.select(slateRange)
diff --git a/packages/editor/src/editor/create-editable-api.ts b/packages/editor/src/editor/create-editable-api.ts
index ded6ae1c0..47a70c017 100644
--- a/packages/editor/src/editor/create-editable-api.ts
+++ b/packages/editor/src/editor/create-editable-api.ts
@@ -4,6 +4,7 @@ import {
   type PortableTextChild,
   type PortableTextObject,
 } from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import {
   isListItemActive,
   isStyleActive,
@@ -249,7 +250,7 @@ export function createEditableAPI(
         return [undefined, undefined]
       }
 
-      const blockIndex = editor.blockIndexMap.get(blockKey)
+      const blockIndex = getIndexForKey(editor.children as Array<PortableTextBlock>, blockKey)
 
       if (blockIndex === undefined) {
         return [undefined, undefined]
@@ -502,7 +503,6 @@ export function createEditableAPI(
           value: editor.children as Array<PortableTextBlock>,
           selection: selectionA,
         },
-        blockIndexMap: editor.blockIndexMap,
       })
       const rangeB = toSlateRange({
         context: {
@@ -510,7 +510,6 @@ export function createEditableAPI(
           value: editor.children as Array<PortableTextBlock>,
           selection: selectionB,
         },
-        blockIndexMap: editor.blockIndexMap,
       })
 
       // Make sure the ranges are valid
diff --git a/packages/editor/src/editor/editor-selector.ts b/packages/editor/src/editor/editor-selector.ts
index 277f1abee..4dd866f2c 100644
--- a/packages/editor/src/editor/editor-selector.ts
+++ b/packages/editor/src/editor/editor-selector.ts
@@ -76,7 +76,6 @@ export function getEditorSnapshot({
     : null
 
   return {
-    blockIndexMap: slateEditorInstance.blockIndexMap,
     context: {
       converters: [...editorActorSnapshot.context.converters],
       keyGenerator: editorActorSnapshot.context.keyGenerator,
diff --git a/packages/editor/src/editor/editor-snapshot.ts b/packages/editor/src/editor/editor-snapshot.ts
index d00f53157..8c2dc3fc5 100644
--- a/packages/editor/src/editor/editor-snapshot.ts
+++ b/packages/editor/src/editor/editor-snapshot.ts
@@ -22,7 +22,6 @@ export type EditorContext = {
  */
 export type EditorSnapshot = {
   context: EditorContext
-  blockIndexMap: Map<string, number>
   /**
    * @beta
    * Subject to change
@@ -61,7 +60,6 @@ export function createEditorSnapshot({
   } satisfies EditorContext
 
   return {
-    blockIndexMap: editor.blockIndexMap,
     context,
     decoratorState: editor.decoratorState,
   } satisfies EditorSnapshot
diff --git a/packages/editor/src/editor/range-decorations-machine.ts b/packages/editor/src/editor/range-decorations-machine.ts
index ce836e538..10965d8e1 100644
--- a/packages/editor/src/editor/range-decorations-machine.ts
+++ b/packages/editor/src/editor/range-decorations-machine.ts
@@ -100,7 +100,6 @@ export const rangeDecorationsMachine = setup({
             value: context.slateEditor.children as Array<PortableTextBlock>,
             selection: rangeDecoration.selection,
           },
-          blockIndexMap: context.slateEditor.blockIndexMap,
         })
 
         if (!Range.isRange(slateRange)) {
@@ -134,7 +133,6 @@ export const rangeDecorationsMachine = setup({
             value: context.slateEditor.children as Array<PortableTextBlock>,
             selection: rangeDecoration.selection,
           },
-          blockIndexMap: context.slateEditor.blockIndexMap,
         })
 
         if (!Range.isRange(slateRange)) {
@@ -169,7 +167,6 @@ export const rangeDecorationsMachine = setup({
             value: context.slateEditor.children as Array<PortableTextBlock>,
             selection: decoratedRange.rangeDecoration.selection,
           },
-          blockIndexMap: context.slateEditor.blockIndexMap,
         })
 
         if (!Range.isRange(slateRange)) {
diff --git a/packages/editor/src/editor/render.element.tsx b/packages/editor/src/editor/render.element.tsx
index 5ff802350..7df089d83 100644
--- a/packages/editor/src/editor/render.element.tsx
+++ b/packages/editor/src/editor/render.element.tsx
@@ -1,5 +1,6 @@
 import type {PortableTextBlock} from '@portabletext/schema'
 import {isTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import {useSelector} from '@xstate/react'
 import {useContext, type ReactElement} from 'react'
 import type {DropPosition} from '../behaviors/behavior.core.drop-position'
@@ -48,7 +49,7 @@ export function RenderElement(props: {
     )
   }
 
-  const blockIndex = slateStatic.blockIndexMap.get(props.element._key)
+  const blockIndex = getIndexForKey(slateStatic.children as Array<PortableTextBlock>, props.element._key)
   const block =
     blockIndex !== undefined
       ? (slateStatic.children as Array<PortableTextBlock>).at(blockIndex)
diff --git a/packages/editor/src/editor/selection-state-context.tsx b/packages/editor/src/editor/selection-state-context.tsx
index 976acc616..7ff9d7b99 100644
--- a/packages/editor/src/editor/selection-state-context.tsx
+++ b/packages/editor/src/editor/selection-state-context.tsx
@@ -1,3 +1,4 @@
+import {getIndexForKey} from '@sanity/json-match'
 import {useSelector} from '@xstate/react'
 import {createContext, useContext} from 'react'
 import {getFocusChild} from '../selectors'
@@ -111,17 +112,18 @@ export function SelectionStateProvider({
       let selectedBlockKeys: Set<string> = emptySet
 
       if (startBlockKey && endBlockKey) {
-        const startBlockIndex = snapshot.blockIndexMap.get(startBlockKey)
-        const endBlockIndex = snapshot.blockIndexMap.get(endBlockKey)
+        const startBlockIndex = getIndexForKey(snapshot.context.value, startBlockKey)
+        const endBlockIndex = getIndexForKey(snapshot.context.value, endBlockKey)
 
         if (startBlockIndex !== undefined && endBlockIndex !== undefined) {
           const minIndex = Math.min(startBlockIndex, endBlockIndex)
           const maxIndex = Math.max(startBlockIndex, endBlockIndex)
           selectedBlockKeys = new Set<string>()
 
-          for (const [key, index] of snapshot.blockIndexMap) {
-            if (index >= minIndex && index <= maxIndex) {
-              selectedBlockKeys.add(key)
+          for (const block of snapshot.context.value) {
+            const index = getIndexForKey(snapshot.context.value, block._key)
+            if (index !== undefined && index >= minIndex && index <= maxIndex) {
+              selectedBlockKeys.add(block._key)
             }
           }
         }
diff --git a/packages/editor/src/internal-utils/create-test-snapshot.ts b/packages/editor/src/internal-utils/create-test-snapshot.ts
index a5192ac78..bacfe0c60 100644
--- a/packages/editor/src/internal-utils/create-test-snapshot.ts
+++ b/packages/editor/src/internal-utils/create-test-snapshot.ts
@@ -14,14 +14,8 @@ export function createTestSnapshot(snapshot: {
     value: snapshot.context?.value ?? [],
     selection: snapshot.context?.selection ?? null,
   }
-  const blockIndexMap = new Map<string, number>()
-
-  snapshot.context?.value?.forEach((block, index) => {
-    blockIndexMap.set(block._key, index)
-  })
 
   return {
-    blockIndexMap,
     context,
     decoratorState: snapshot?.decoratorState ?? {},
   }
diff --git a/packages/editor/src/internal-utils/to-slate-range.test.ts b/packages/editor/src/internal-utils/to-slate-range.test.ts
index 317ff8e10..66d3bbecc 100644
--- a/packages/editor/src/internal-utils/to-slate-range.test.ts
+++ b/packages/editor/src/internal-utils/to-slate-range.test.ts
@@ -55,7 +55,6 @@ describe(toSlateRange.name, () => {
           },
         },
       },
-      blockIndexMap: new Map([[blockKey, 0]]),
     })
 
     expect(range).toEqual({
@@ -104,7 +103,6 @@ describe(toSlateRange.name, () => {
           },
         },
       },
-      blockIndexMap: new Map([[blockKey, 0]]),
     })
 
     expect(range).toEqual({
@@ -137,7 +135,6 @@ describe(toSlateRange.name, () => {
           },
         },
       },
-      blockIndexMap: new Map([[blockObjectKey, 0]]),
     })
 
     expect(range).toEqual({
@@ -179,7 +176,6 @@ describe(toSlateRange.name, () => {
           },
         },
       },
-      blockIndexMap: new Map([[blockKey, 0]]),
     })
 
     expect(range).toEqual({
@@ -220,7 +216,6 @@ describe(toSlateRange.name, () => {
           },
         },
       },
-      blockIndexMap: new Map([[blockKey, 0]]),
     })
 
     expect(range).toEqual({
@@ -267,7 +262,6 @@ describe(toSlateRange.name, () => {
           },
         },
       },
-      blockIndexMap: new Map([[blockKey, 0]]),
     })
 
     expect(range).toEqual({
diff --git a/packages/editor/src/internal-utils/to-slate-range.ts b/packages/editor/src/internal-utils/to-slate-range.ts
index 766a23157..56a10bb7a 100644
--- a/packages/editor/src/internal-utils/to-slate-range.ts
+++ b/packages/editor/src/internal-utils/to-slate-range.ts
@@ -4,7 +4,8 @@ import {
   type PortableTextObject,
   type PortableTextSpan,
 } from '@portabletext/schema'
-import type {EditorContext, EditorSnapshot} from '../editor/editor-snapshot'
+import {getIndexForKey} from '@sanity/json-match'
+import type {EditorContext} from '../editor/editor-snapshot'
 import type {Path, Range} from '../slate'
 import type {EditorSelectionPoint} from '../types/editor'
 import {blockOffsetToSpanSelectionPoint} from '../utils/util.block-offset'
@@ -14,11 +15,9 @@ import {
   getChildKeyFromSelectionPoint,
 } from '../utils/util.selection-point'
 
-export function toSlateRange(
-  snapshot: {
-    context: Pick<EditorContext, 'schema' | 'value' | 'selection'>
-  } & Pick<EditorSnapshot, 'blockIndexMap'>,
-): Range | null {
+export function toSlateRange(snapshot: {
+  context: Pick<EditorContext, 'schema' | 'value' | 'selection'>
+}): Range | null {
   if (!snapshot.context.selection) {
     return null
   }
@@ -69,7 +68,7 @@ export function toSlateRange(
 export function toSlateSelectionPoint(
   snapshot: {
     context: Pick<EditorContext, 'schema' | 'value'>
-  } & Pick<EditorSnapshot, 'blockIndexMap'>,
+  },
   selectionPoint: EditorSelectionPoint,
   direction: 'forward' | 'backward',
 ):
@@ -84,7 +83,7 @@ export function toSlateSelectionPoint(
     return undefined
   }
 
-  const blockIndex = snapshot.blockIndexMap.get(blockKey)
+  const blockIndex = getIndexForKey(snapshot.context.value, blockKey)
 
   if (blockIndex === undefined) {
     return undefined
diff --git a/packages/editor/src/operations/operation.annotation.add.ts b/packages/editor/src/operations/operation.annotation.add.ts
index 3d8955e0a..996f24dda 100644
--- a/packages/editor/src/operations/operation.annotation.add.ts
+++ b/packages/editor/src/operations/operation.annotation.add.ts
@@ -35,7 +35,6 @@ export const addAnnotationOperationImplementation: OperationImplementation<
           value: operation.editor.children as Array<PortableTextBlock>,
           selection: operation.at,
         },
-        blockIndexMap: operation.editor.blockIndexMap,
       })
     : null
 
diff --git a/packages/editor/src/operations/operation.annotation.remove.ts b/packages/editor/src/operations/operation.annotation.remove.ts
index 9e8e6b02e..8f402ac0e 100644
--- a/packages/editor/src/operations/operation.annotation.remove.ts
+++ b/packages/editor/src/operations/operation.annotation.remove.ts
@@ -18,7 +18,6 @@ export const removeAnnotationOperationImplementation: OperationImplementation<
           value: operation.editor.children as Array<PortableTextBlock>,
           selection: operation.at,
         },
-        blockIndexMap: operation.editor.blockIndexMap,
       })
     : null
 
diff --git a/packages/editor/src/operations/operation.block.set.ts b/packages/editor/src/operations/operation.block.set.ts
index 1d7b8359a..58431dcbd 100644
--- a/packages/editor/src/operations/operation.block.set.ts
+++ b/packages/editor/src/operations/operation.block.set.ts
@@ -1,5 +1,6 @@
 import {applyAll, set} from '@portabletext/patches'
-import {isTextBlock} from '@portabletext/schema'
+import {isTextBlock, type PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import {applySetNode} from '../internal-utils/apply-set-node'
 import {parseMarkDefs} from '../utils/parse-blocks'
 import type {OperationImplementation} from './operation.types'
@@ -7,7 +8,7 @@ import type {OperationImplementation} from './operation.types'
 export const blockSetOperationImplementation: OperationImplementation<
   'block.set'
 > = ({context, operation}) => {
-  const blockIndex = operation.editor.blockIndexMap.get(operation.at[0]._key)
+  const blockIndex = getIndexForKey(operation.editor.children as Array<PortableTextBlock>, operation.at[0]._key)
 
   if (blockIndex === undefined) {
     throw new Error(
diff --git a/packages/editor/src/operations/operation.block.unset.ts b/packages/editor/src/operations/operation.block.unset.ts
index 437e591bd..97fd2ac10 100644
--- a/packages/editor/src/operations/operation.block.unset.ts
+++ b/packages/editor/src/operations/operation.block.unset.ts
@@ -1,4 +1,5 @@
-import {isTextBlock} from '@portabletext/schema'
+import {isTextBlock, type PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import {applySetNode} from '../internal-utils/apply-set-node'
 import type {OperationImplementation} from './operation.types'
 
@@ -6,7 +7,7 @@ export const blockUnsetOperationImplementation: OperationImplementation<
   'block.unset'
 > = ({context, operation}) => {
   const blockKey = operation.at[0]._key
-  const blockIndex = operation.editor.blockIndexMap.get(blockKey)
+  const blockIndex = getIndexForKey(operation.editor.children as Array<PortableTextBlock>, blockKey)
 
   if (blockIndex === undefined) {
     throw new Error(`Unable to find block index for block key ${blockKey}`)
diff --git a/packages/editor/src/operations/operation.child.set.ts b/packages/editor/src/operations/operation.child.set.ts
index 4536dea4e..17fb97d3a 100644
--- a/packages/editor/src/operations/operation.child.set.ts
+++ b/packages/editor/src/operations/operation.child.set.ts
@@ -16,7 +16,6 @@ export const childSetOperationImplementation: OperationImplementation<
         focus: {path: operation.at, offset: 0},
       },
     },
-    blockIndexMap: operation.editor.blockIndexMap,
   })
 
   if (!location) {
diff --git a/packages/editor/src/operations/operation.child.unset.ts b/packages/editor/src/operations/operation.child.unset.ts
index bbd7e3c4e..671739484 100644
--- a/packages/editor/src/operations/operation.child.unset.ts
+++ b/packages/editor/src/operations/operation.child.unset.ts
@@ -1,5 +1,6 @@
 import type {PortableTextBlock} from '@portabletext/schema'
 import {isTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import {applySetNode} from '../internal-utils/apply-set-node'
 import {Editor} from '../slate'
 import type {OperationImplementation} from './operation.types'
@@ -8,7 +9,7 @@ export const childUnsetOperationImplementation: OperationImplementation<
   'child.unset'
 > = ({context, operation}) => {
   const blockKey = operation.at[0]._key
-  const blockIndex = operation.editor.blockIndexMap.get(blockKey)
+  const blockIndex = getIndexForKey(operation.editor.children as Array<PortableTextBlock>, blockKey)
 
   if (blockIndex === undefined) {
     throw new Error(`Unable to find block index for block key ${blockKey}`)
diff --git a/packages/editor/src/operations/operation.decorator.add.ts b/packages/editor/src/operations/operation.decorator.add.ts
index 43f54f004..7f0e670fc 100644
--- a/packages/editor/src/operations/operation.decorator.add.ts
+++ b/packages/editor/src/operations/operation.decorator.add.ts
@@ -19,7 +19,6 @@ export const decoratorAddOperationImplementation: OperationImplementation<
           value: operation.editor.children as Array<PortableTextBlock>,
           selection: operation.at,
         },
-        blockIndexMap: operation.editor.blockIndexMap,
       })
     : operation.editor.selection
 
diff --git a/packages/editor/src/operations/operation.decorator.remove.ts b/packages/editor/src/operations/operation.decorator.remove.ts
index db4af3b2e..93d62c3f9 100644
--- a/packages/editor/src/operations/operation.decorator.remove.ts
+++ b/packages/editor/src/operations/operation.decorator.remove.ts
@@ -17,7 +17,6 @@ export const decoratorRemoveOperationImplementation: OperationImplementation<
           value: operation.editor.children as Array<PortableTextBlock>,
           selection: operation.at,
         },
-        blockIndexMap: operation.editor.blockIndexMap,
       })
     : editor.selection
 
diff --git a/packages/editor/src/operations/operation.delete.ts b/packages/editor/src/operations/operation.delete.ts
index d2d06df08..922c1bd70 100644
--- a/packages/editor/src/operations/operation.delete.ts
+++ b/packages/editor/src/operations/operation.delete.ts
@@ -26,7 +26,6 @@ export const deleteOperationImplementation: OperationImplementation<
           value: operation.editor.children as Array<PortableTextBlock>,
           selection: operation.at,
         },
-        blockIndexMap: operation.editor.blockIndexMap,
       })
     : operation.editor.selection
 
diff --git a/packages/editor/src/operations/operation.insert.block.ts b/packages/editor/src/operations/operation.insert.block.ts
index b560d6179..1663868b0 100644
--- a/packages/editor/src/operations/operation.insert.block.ts
+++ b/packages/editor/src/operations/operation.insert.block.ts
@@ -68,7 +68,6 @@ export function insertBlock(options: {
           value: editor.children as Array<PortableTextBlock>,
           selection: options.at,
         },
-        blockIndexMap: editor.blockIndexMap,
       })
     : editor.selection
 
diff --git a/packages/editor/src/operations/operation.move.block.ts b/packages/editor/src/operations/operation.move.block.ts
index 468d291b2..0e1187264 100644
--- a/packages/editor/src/operations/operation.move.block.ts
+++ b/packages/editor/src/operations/operation.move.block.ts
@@ -1,3 +1,5 @@
+import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import {applyMoveNode} from '../internal-utils/apply-move-node'
 import {getBlockKeyFromSelectionPoint} from '../utils/util.selection-point'
 import type {OperationImplementation} from './operation.types'
@@ -14,7 +16,7 @@ export const moveBlockOperationImplementation: OperationImplementation<
     throw new Error('Failed to get block key from selection point')
   }
 
-  const originBlockIndex = operation.editor.blockIndexMap.get(originKey)
+  const originBlockIndex = getIndexForKey(operation.editor.children as Array<PortableTextBlock>, originKey)
 
   if (originBlockIndex === undefined) {
     throw new Error('Failed to get block index from block key')
@@ -29,8 +31,10 @@ export const moveBlockOperationImplementation: OperationImplementation<
     throw new Error('Failed to get block key from selection point')
   }
 
-  const destinationBlockIndex =
-    operation.editor.blockIndexMap.get(destinationKey)
+  const destinationBlockIndex = getIndexForKey(
+    operation.editor.children as Array<PortableTextBlock>,
+    destinationKey,
+  )
 
   if (destinationBlockIndex === undefined) {
     throw new Error('Failed to get block index from block key')
diff --git a/packages/editor/src/operations/operation.select.ts b/packages/editor/src/operations/operation.select.ts
index 3bb3d5799..6c299f373 100644
--- a/packages/editor/src/operations/operation.select.ts
+++ b/packages/editor/src/operations/operation.select.ts
@@ -12,7 +12,6 @@ export const selectOperationImplementation: OperationImplementation<
       value: operation.editor.children as Array<PortableTextBlock>,
       selection: operation.at,
     },
-    blockIndexMap: operation.editor.blockIndexMap,
   })
 
   if (newSelection) {
diff --git a/packages/editor/src/selectors/selector.get-anchor-block.ts b/packages/editor/src/selectors/selector.get-anchor-block.ts
index 7bd699c4f..09a67eba9 100644
--- a/packages/editor/src/selectors/selector.get-anchor-block.ts
+++ b/packages/editor/src/selectors/selector.get-anchor-block.ts
@@ -1,4 +1,5 @@
 import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {BlockPath} from '../types/paths'
 import {getBlockKeyFromSelectionPoint} from '../utils/util.selection-point'
@@ -14,7 +15,7 @@ export const getAnchorBlock: EditorSelector<
   }
 
   const key = getBlockKeyFromSelectionPoint(snapshot.context.selection.anchor)
-  const index = key ? snapshot.blockIndexMap.get(key) : undefined
+  const index = key ? getIndexForKey(snapshot.context.value, key) : undefined
   const node =
     index !== undefined ? snapshot.context.value.at(index) : undefined
 
diff --git a/packages/editor/src/selectors/selector.get-focus-block.ts b/packages/editor/src/selectors/selector.get-focus-block.ts
index 3889ecfbe..6f83cf2a9 100644
--- a/packages/editor/src/selectors/selector.get-focus-block.ts
+++ b/packages/editor/src/selectors/selector.get-focus-block.ts
@@ -1,4 +1,5 @@
 import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {BlockPath} from '../types/paths'
 import {getBlockKeyFromSelectionPoint} from '../utils/util.selection-point'
@@ -14,7 +15,7 @@ export const getFocusBlock: EditorSelector<
   }
 
   const key = getBlockKeyFromSelectionPoint(snapshot.context.selection.focus)
-  const index = key ? snapshot.blockIndexMap.get(key) : undefined
+  const index = key ? getIndexForKey(snapshot.context.value, key) : undefined
 
   const node =
     index !== undefined ? snapshot.context.value.at(index) : undefined
diff --git a/packages/editor/src/selectors/selector.get-next-block.ts b/packages/editor/src/selectors/selector.get-next-block.ts
index 86fc2d795..84761c468 100644
--- a/packages/editor/src/selectors/selector.get-next-block.ts
+++ b/packages/editor/src/selectors/selector.get-next-block.ts
@@ -1,4 +1,5 @@
 import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {BlockPath} from '../types/paths'
 import {getSelectionEndBlock} from './selector.get-selection-end-block'
@@ -15,9 +16,12 @@ export const getNextBlock: EditorSelector<
     return undefined
   }
 
-  const index = snapshot.blockIndexMap.get(selectionEndBlock.node._key)
+  const index = getIndexForKey(
+    snapshot.context.value,
+    selectionEndBlock.node._key,
+  )
 
-  if (index === undefined || index === snapshot.context.value.length - 1) {
+  if (index === undefined) {
     return undefined
   }
 
diff --git a/packages/editor/src/selectors/selector.get-previous-block.ts b/packages/editor/src/selectors/selector.get-previous-block.ts
index 895a332b9..44cd9b593 100644
--- a/packages/editor/src/selectors/selector.get-previous-block.ts
+++ b/packages/editor/src/selectors/selector.get-previous-block.ts
@@ -1,4 +1,5 @@
 import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {BlockPath} from '../types/paths'
 import {getSelectionStartBlock} from './selector.get-selection-start-block'
@@ -15,7 +16,10 @@ export const getPreviousBlock: EditorSelector<
     return undefined
   }
 
-  const index = snapshot.blockIndexMap.get(selectionStartBlock.node._key)
+  const index = getIndexForKey(
+    snapshot.context.value,
+    selectionStartBlock.node._key,
+  )
 
   if (index === undefined || index === 0) {
     return undefined
diff --git a/packages/editor/src/selectors/selector.get-selected-blocks.ts b/packages/editor/src/selectors/selector.get-selected-blocks.ts
index 46de71730..0150f22d6 100644
--- a/packages/editor/src/selectors/selector.get-selected-blocks.ts
+++ b/packages/editor/src/selectors/selector.get-selected-blocks.ts
@@ -1,4 +1,5 @@
 import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {BlockPath} from '../types/paths'
 import {getSelectionEndPoint} from '../utils/util.get-selection-end-point'
@@ -25,8 +26,8 @@ export const getSelectedBlocks: EditorSelector<
     return selectedBlocks
   }
 
-  const startBlockIndex = snapshot.blockIndexMap.get(startKey)
-  const endBlockIndex = snapshot.blockIndexMap.get(endKey)
+  const startBlockIndex = getIndexForKey(snapshot.context.value, startKey)
+  const endBlockIndex = getIndexForKey(snapshot.context.value, endKey)
 
   if (startBlockIndex === undefined || endBlockIndex === undefined) {
     return selectedBlocks
diff --git a/packages/editor/src/selectors/selector.get-selected-children.ts b/packages/editor/src/selectors/selector.get-selected-children.ts
index 5ce2e023c..118a07af3 100644
--- a/packages/editor/src/selectors/selector.get-selected-children.ts
+++ b/packages/editor/src/selectors/selector.get-selected-children.ts
@@ -1,5 +1,6 @@
 import {isSpan, isTextBlock} from '@portabletext/schema'
 import type {PortableTextChild} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {ChildPath} from '../types/paths'
 import {
@@ -44,8 +45,8 @@ export function getSelectedChildren<
       return []
     }
 
-    const startBlockIndex = snapshot.blockIndexMap.get(startBlockKey)
-    const endBlockIndex = snapshot.blockIndexMap.get(endBlockKey)
+    const startBlockIndex = getIndexForKey(snapshot.context.value, startBlockKey)
+    const endBlockIndex = getIndexForKey(snapshot.context.value, endBlockKey)
 
     if (startBlockIndex === undefined || endBlockIndex === undefined) {
       return []
diff --git a/packages/editor/src/selectors/selector.get-selected-text-blocks.ts b/packages/editor/src/selectors/selector.get-selected-text-blocks.ts
index aefc55720..7202c8ebc 100644
--- a/packages/editor/src/selectors/selector.get-selected-text-blocks.ts
+++ b/packages/editor/src/selectors/selector.get-selected-text-blocks.ts
@@ -1,4 +1,5 @@
 import {isTextBlock, type PortableTextTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import type {BlockPath} from '../types/paths'
 import {getSelectionEndPoint} from '../utils/util.get-selection-end-point'
@@ -29,8 +30,8 @@ export const getSelectedTextBlocks: EditorSelector<
     return selectedTextBlocks
   }
 
-  const startBlockIndex = snapshot.blockIndexMap.get(startBlockKey)
-  const endBlockIndex = snapshot.blockIndexMap.get(endBlockKey)
+  const startBlockIndex = getIndexForKey(snapshot.context.value, startBlockKey)
+  const endBlockIndex = getIndexForKey(snapshot.context.value, endBlockKey)
 
   if (startBlockIndex === undefined || endBlockIndex === undefined) {
     return selectedTextBlocks
diff --git a/packages/editor/src/selectors/selector.get-selected-value.ts b/packages/editor/src/selectors/selector.get-selected-value.ts
index 7c3e950cb..94731b424 100644
--- a/packages/editor/src/selectors/selector.get-selected-value.ts
+++ b/packages/editor/src/selectors/selector.get-selected-value.ts
@@ -1,4 +1,5 @@
 import type {PortableTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelector} from '../editor/editor-selector'
 import {getSelectionEndPoint} from '../utils/util.get-selection-end-point'
 import {getSelectionStartPoint} from '../utils/util.get-selection-start-point'
@@ -26,8 +27,8 @@ export const getSelectedValue: EditorSelector<Array<PortableTextBlock>> = (
     return []
   }
 
-  const startBlockIndex = snapshot.blockIndexMap.get(startBlockKey)
-  const endBlockIndex = snapshot.blockIndexMap.get(endBlockKey)
+  const startBlockIndex = getIndexForKey(snapshot.context.value, startBlockKey)
+  const endBlockIndex = getIndexForKey(snapshot.context.value, endBlockKey)
 
   if (startBlockIndex === undefined || endBlockIndex === undefined) {
     return []
diff --git a/packages/editor/src/selectors/selector.is-overlapping-selection.ts b/packages/editor/src/selectors/selector.is-overlapping-selection.ts
index 23a53ea34..f4975c046 100644
--- a/packages/editor/src/selectors/selector.is-overlapping-selection.ts
+++ b/packages/editor/src/selectors/selector.is-overlapping-selection.ts
@@ -1,3 +1,4 @@
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSelection, EditorSelectionPoint} from '../types/editor'
 import {
   getSelectionEndPoint,
@@ -43,15 +44,20 @@ export function isOverlappingSelection(
       return false
     }
 
-    const selectionStartBlockIndex = snapshot.blockIndexMap.get(
+    const selectionStartBlockIndex = getIndexForKey(
+      snapshot.context.value,
       selectionStartBlockKey,
     )
-    const selectionEndBlockIndex =
-      snapshot.blockIndexMap.get(selectionEndBlockKey)
-    const editorSelectionStartBlockIndex = snapshot.blockIndexMap.get(
+    const selectionEndBlockIndex = getIndexForKey(
+      snapshot.context.value,
+      selectionEndBlockKey,
+    )
+    const editorSelectionStartBlockIndex = getIndexForKey(
+      snapshot.context.value,
       editorSelectionStartBlockKey,
     )
-    const editorSelectionEndBlockIndex = snapshot.blockIndexMap.get(
+    const editorSelectionEndBlockIndex = getIndexForKey(
+      snapshot.context.value,
       editorSelectionEndBlockKey,
     )
 
diff --git a/packages/editor/src/slate-plugins/slate-plugin.unique-keys.ts b/packages/editor/src/slate-plugins/slate-plugin.unique-keys.ts
index 6fd8f53dd..392ec921f 100644
--- a/packages/editor/src/slate-plugins/slate-plugin.unique-keys.ts
+++ b/packages/editor/src/slate-plugins/slate-plugin.unique-keys.ts
@@ -1,7 +1,8 @@
 import type {PortableTextBlock} from '@portabletext/schema'
 import {isTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorActor} from '../editor/editor-machine'
-import type {EditorContext, EditorSnapshot} from '../editor/editor-snapshot'
+import type {EditorContext} from '../editor/editor-snapshot'
 import {applySetNode} from '../internal-utils/apply-set-node'
 import {Editor, Element, Node, type Path} from '../slate'
 import type {PortableTextSlateEditor} from '../types/slate-editor'
@@ -47,7 +48,6 @@ export function createUniqueKeysPlugin(editorActor: EditorActor) {
             operation.node._key &&
             keyExistsAtPath(
               {
-                blockIndexMap: editor.blockIndexMap,
                 context: {
                   schema: context.schema,
                   value: editor.children as Array<PortableTextBlock>,
@@ -178,14 +178,14 @@ export function createUniqueKeysPlugin(editorActor: EditorActor) {
 }
 
 function keyExistsAtPath(
-  snapshot: Pick<EditorSnapshot, 'blockIndexMap'> & {
+  snapshot: {
     context: Pick<EditorContext, 'schema' | 'value'>
   },
   path: Path,
   key: string,
 ): boolean {
   if (path.length === 1) {
-    return snapshot.blockIndexMap.has(key)
+    return getIndexForKey(snapshot.context.value, key) !== undefined
   }
 
   if (path.length > 2) {
diff --git a/packages/editor/src/utils/util.compare-points.ts b/packages/editor/src/utils/util.compare-points.ts
index 574477981..de8912b74 100644
--- a/packages/editor/src/utils/util.compare-points.ts
+++ b/packages/editor/src/utils/util.compare-points.ts
@@ -1,4 +1,5 @@
 import {isTextBlock} from '@portabletext/schema'
+import {getIndexForKey} from '@sanity/json-match'
 import type {EditorSnapshot} from '../editor/editor-snapshot'
 import type {EditorSelectionPoint} from '../types/editor'
 import {
@@ -29,8 +30,8 @@ export function comparePoints(
     throw new Error(`Cannot compare points: no block key found for ${pointB}`)
   }
 
-  const blockIndexA = snapshot.blockIndexMap.get(blockKeyA)
-  const blockIndexB = snapshot.blockIndexMap.get(blockKeyB)
+  const blockIndexA = getIndexForKey(snapshot.context.value, blockKeyA)
+  const blockIndexB = getIndexForKey(snapshot.context.value, blockKeyB)
 
   if (blockIndexA === undefined) {
     throw new Error(`Cannot compare points: block "${blockKeyA}" not found`)
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 16d589b3d..612dd851f 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -438,6 +438,9 @@ importers:
       '@portabletext/to-html':
         specifier: ^5.0.2
         version: 5.0.2
+      '@sanity/json-match':
+        specifier: ^1.0.5
+        version: 1.0.5
       '@xstate/react':
         specifier: ^6.1.0
         version: 6.1.0(@types/react@19.2.14)(react@19.2.3)(xstate@5.28.0)