diff --git a/html-parse.cabal b/html-parse.cabal
index 6c8b655..2871d9f 100644
--- a/html-parse.cabal
+++ b/html-parse.cabal
@@ -55,6 +55,10 @@ cabal-version:       >=1.10
 tested-with:         GHC==8.4.*, GHC==8.6.*, GHC==8.8.*, GHC==8.10.*, GHC==9.0.*, GHC==9.2.*, GHC==9.4.*
 extra-source-files:  changelog.md
 
+flag case-insensitive
+  Description: Implement case insensitive HTML tags.
+  Default: True
+  Manual: True
 
 source-repository head
   type:                git
@@ -71,13 +75,20 @@ library
                        attoparsec >=0.13 && <0.15,
                        text >=1.2 && <2.1,
                        containers >=0.5 && <0.7
+  if flag(case-insensitive)
+    build-depends:     case-insensitive
+    cpp-options:       -DCASE_INSENSITIVE=1
   default-language:    Haskell2010
 
 benchmark bench
   type:                exitcode-stdio-1.0
   main-is:             Benchmark.hs
   other-extensions:    OverloadedStrings, DeriveGeneric
+  if flag(case-insensitive)
+    build-depends:     case-insensitive
+    cpp-options:       -DCASE_INSENSITIVE=1
   build-depends:       base,
+                       bytestring,
                        deepseq,
                        attoparsec,
                        text,
@@ -92,6 +103,9 @@ test-suite spec
   main-is:             Spec.hs
   other-modules:       Text.HTML.ParserSpec, Text.HTML.TreeSpec
   ghc-options:         -Wall -with-rtsopts=-T
+  if flag(case-insensitive)
+    build-depends:     case-insensitive
+    cpp-options:       -DCASE_INSENSITIVE=1
   build-tool-depends:  hspec-discover:hspec-discover
   build-depends:       base,
                        containers,
diff --git a/src/Text/HTML/Parser.hs b/src/Text/HTML/Parser.hs
index 0776d45..435ba84 100644
--- a/src/Text/HTML/Parser.hs
+++ b/src/Text/HTML/Parser.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE LambdaCase #-}
@@ -32,6 +33,9 @@ import Control.Applicative
 import Data.Monoid
 import Control.Monad (guard)
 import Control.DeepSeq
+#if CASE_INSENSITIVE
+import Data.CaseInsensitive (CI, mk, original)
+#endif
 
 import Data.Attoparsec.Text
 import qualified Data.Attoparsec.Text.Lazy as AL
@@ -48,7 +52,15 @@ import qualified Data.Trie as Trie
 -- Section numbers refer to W3C HTML 5.2 specification.
 
 -- | A tag name (e.g. @body@)
+#if CASE_INSENSITIVE
+type TagName   = CI Text
+#else
 type TagName   = Text
+original :: TagName -> Text
+original = id
+mk :: Text -> TagName
+mk = id
+#endif
 
 -- | An attribute name (e.g. @href@)
 type AttrName  = Text
@@ -139,6 +151,7 @@ isWhitespace :: Char -> Bool
 isWhitespace '\x09' = True
 isWhitespace '\x0a' = True
 isWhitespace '\x0c' = True
+isWhitespace '\x0d' = True
 isWhitespace ' '    = True
 isWhitespace _      = False
 
@@ -169,8 +182,8 @@ tagNameClose = do
 -- | /§8.2.4.10/: Tag name state: common code
 --
 -- deviation: no lower-casing, don't handle NULL characters
-tagName' :: Parser Text
-tagName' = do
+tagName' :: Parser TagName
+tagName' = mk <$> do
     c <- peekChar'
     guard $ isAsciiUpper c || isAsciiLower c
     takeWhile $ not . (isWhitespace `orC` isC '/' `orC` isC '<' `orC` isC '>')
@@ -395,10 +408,10 @@ renderTokens = mconcat . fmap renderToken
 -- | (Somewhat) canonical string representation of 'Token'.
 renderToken :: Token -> TL.Text
 renderToken = TL.fromStrict . mconcat . \case
-    (TagOpen n [])         -> ["<", n, ">"]
-    (TagOpen n attrs)      -> ["<", n, " ", renderAttrs attrs, ">"]
-    (TagSelfClose n attrs) -> ["<", n, " ", renderAttrs attrs, " />"]
-    (TagClose n)           -> ["</", n, ">"]
+    (TagOpen n [])         -> ["<", original n, ">"]
+    (TagOpen n attrs)      -> ["<", original n, " ", renderAttrs attrs, ">"]
+    (TagSelfClose n attrs) -> ["<", original n, " ", renderAttrs attrs, " />"]
+    (TagClose n)           -> ["</", original n, ">"]
     (ContentChar c)        -> [T.singleton c]
     (ContentText t)        -> [t]
     (Comment builder)      -> ["<!--", TL.toStrict $ B.toLazyText builder, "-->"]
diff --git a/src/Text/HTML/Tree.hs b/src/Text/HTML/Tree.hs
index b1bfa85..2024a3d 100644
--- a/src/Text/HTML/Tree.hs
+++ b/src/Text/HTML/Tree.hs
@@ -48,7 +48,7 @@ tokensToForest = f (PStack [] [])
 -- @ nonClosing = ["br", "hr", "img", "meta", "area", "base", "col", "embed", "input", "link", "param", "source", "track", "wbr"] @
 --
 -- <https:\/\/www.w3.org\/TR\/html52\/syntax.html#void-elements>
-nonClosing :: [Text]
+nonClosing :: [TagName]
 nonClosing = ["br", "hr", "img", "meta", "area", "base", "col", "embed", "input", "link", "param", "source", "track", "wbr"]
 
 data ParseTokenForestError =
diff --git a/tests/Text/HTML/ParserSpec.hs b/tests/Text/HTML/ParserSpec.hs
index 9f5a64a..c47772b 100644
--- a/tests/Text/HTML/ParserSpec.hs
+++ b/tests/Text/HTML/ParserSpec.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                        #-}
 {-# LANGUAGE GADTs                      #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE OverloadedStrings          #-}
@@ -20,6 +21,11 @@ import           Test.QuickCheck
 import           Test.QuickCheck.Instances ()
 import           Text.HTML.Parser
 
+#if CASE_INSENSITIVE
+import Data.CaseInsensitive
+#else
+mk = id
+#endif
 
 instance Arbitrary Token where
   arbitrary = oneof [validOpen, validClose, validFlat]
@@ -60,11 +66,11 @@ validXmlChar = elements (['\x20'..'\x7E'] \\ "\x09\x0a\x0c &/<>")
 validXmlText :: Gen T.Text
 validXmlText = T.pack <$> sized (`maxListOf` validXmlChar)
 
-validXmlTagName :: Gen T.Text
+validXmlTagName :: Gen TagName
 validXmlTagName = do
     initchar  <- elements $ ['a'..'z'] <> ['A'..'Z']
     thenchars <- sized (`maxListOf` elements (['\x20'..'\x7E'] \\ "\x09\x0a\x0c &/<>"))
-    pure . T.pack $ initchar : thenchars
+    pure . mk . T.pack $ initchar : thenchars
 
 validXmlAttrName :: Gen T.Text
 validXmlAttrName = do