diff --git a/data/examples/declaration/value/function/unboxed-string-lit-out.hs b/data/examples/declaration/value/function/unboxed-string-lit-out.hs
new file mode 100644
index 0000000..36ebb7c
--- /dev/null
+++ b/data/examples/declaration/value/function/unboxed-string-lit-out.hs
@@ -0,0 +1,3 @@
+{-# LANGUAGE MagicHash #-}
+
+main = new "p"#
diff --git a/data/examples/declaration/value/function/unboxed-string-lit.hs b/data/examples/declaration/value/function/unboxed-string-lit.hs
new file mode 100644
index 0000000..36ebb7c
--- /dev/null
+++ b/data/examples/declaration/value/function/unboxed-string-lit.hs
@@ -0,0 +1,3 @@
+{-# LANGUAGE MagicHash #-}
+
+main = new "p"#
diff --git a/ormolu.cabal b/ormolu.cabal
index 90ddeb5..feee5ac 100644
--- a/ormolu.cabal
+++ b/ormolu.cabal
@@ -38,6 +38,7 @@ flag dev
 library
   hs-source-dirs:     src
   build-depends:      base           >= 4.12 && < 5.0
+                    , bytestring     >= 0.2 && < 0.11
                     , containers     >= 0.5 && < 0.7
                     , dlist          >= 0.8 && < 0.9
                     , exceptions     >= 0.6 && < 0.11
diff --git a/src/Ormolu/Diff.hs b/src/Ormolu/Diff.hs
index 46b39ba..1281c4c 100644
--- a/src/Ormolu/Diff.hs
+++ b/src/Ormolu/Diff.hs
@@ -11,6 +11,7 @@ module Ormolu.Diff
 where
 
 import BasicTypes (SourceText)
+import Data.ByteString (ByteString)
 import Data.Generics
 import GHC
 import Ormolu.Imports (sortImports)
@@ -51,6 +52,12 @@ matchIgnoringSrcSpans = genericQuery
   where
     genericQuery :: GenericQ (GenericQ Diff)
     genericQuery x y
+      -- NOTE 'ByteString' implement 'Data' instance manually and does not
+      -- implement 'toConstr', so we have to deal with it in a special way.
+      | Just x' <- cast x, Just y' <- cast y =
+        if x' == (y' :: ByteString)
+          then Same
+          else Different []
       | typeOf x == typeOf y, toConstr x == toConstr y =
           mconcat $ gzipWithQ
             (genericQuery