diff --git a/content/base/src/nsDocument.h b/content/base/src/nsDocument.h
index 197ac9cccdb..a38f0a88588 100644
--- a/content/base/src/nsDocument.h
+++ b/content/base/src/nsDocument.h
@@ -310,8 +310,8 @@ public:
     static KeyTypePointer KeyToPointer(KeyType& aKey) { return &aKey; }
     static PLDHashNumber HashKey(KeyTypePointer aKey)
     {
-      return NS_PTR_TO_INT32(aKey->mCallback) >> 2 +
-             NS_PTR_TO_INT32(aKey->mData);
+      return (NS_PTR_TO_INT32(aKey->mCallback) >> 2) ^
+             (NS_PTR_TO_INT32(aKey->mData));
     }
     enum { ALLOW_MEMMOVE = PR_TRUE };