diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Revision history for recover-rtti
 
+## 0.5.2 -- 2025-12-16
+
+* Support `unordered-containers-0.2.21` (Brandon Chinn, #45)
+
 ## 0.5.1 -- 2025-07-19
 
 * Relax bounds, including support for `QuickCheck-2.16`
diff --git a/recover-rtti.cabal b/recover-rtti.cabal
--- a/recover-rtti.cabal
+++ b/recover-rtti.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               recover-rtti
-version:            0.5.1
+version:            0.5.2
 synopsis:           Recover run-time type information from the GHC heap
 description:        The main function in this package is 'classify', which looks
                     at the GHC heap to recover type information about arbitrary
diff --git a/src/Debug/RecoverRTTI/Classify.hs b/src/Debug/RecoverRTTI/Classify.hs
--- a/src/Debug/RecoverRTTI/Classify.hs
+++ b/src/Debug/RecoverRTTI/Classify.hs
@@ -1,4 +1,6 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE UnboxedTuples #-}
 
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 
@@ -358,7 +360,9 @@
     classifyArrayLike
       C_HM_Array
       HashMap.Array.length
-      (`HashMap.Array.index` 0)
+      hmHead
+  where
+    hmHead a = case HashMap.Array.index# a 0 of (# x #) -> x
 
 classifyPrimArray ::
      Prim.Array a