diff --git a/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java b/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java
index ea5d9cd0807..86997c347f7 100644
--- a/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java
+++ b/pdfbox/src/main/java/org/apache/pdfbox/multipdf/PDFMergerUtility.java
@@ -795,6 +795,7 @@ else if (destOCP != null && srcOCP != null)
                         if (!srcNumberTreeAsMap.isEmpty())
                         {
                             mergeStructTree = true;
+                            destParentTreeNextKey -= Collections.min(srcNumberTreeAsMap.keySet()); // allow for negative struct parent values
                         }
                     }
                 }
@@ -1498,8 +1499,8 @@ private void updateStructParentEntries(PDPage page, int structParentOffset) thro
         List<PDAnnotation> newannots = new ArrayList<>(annots.size());
         annots.forEach(annot ->
         {
-            int structParent = annot.getStructParent();
-            if (structParent >= 0)
+            int structParent = annot.getCOSObject().getInt(COSName.STRUCT_PARENT, Integer.MIN_VALUE); // allow for negative struct parent values
+            if (structParent > Integer.MIN_VALUE) // allow for negative struct parent values
             {
                 annot.setStructParent(structParent + structParentOffset);
             }