diff --git a/src/lisp.h b/src/lisp.h
index 0f5a5410081..75146bd7715 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -2997,7 +2997,7 @@ SXHASH_REDUCE (EMACS_UINT x)
 reduce_emacs_uint_to_hash_hash (EMACS_UINT x)
 {
   verify (sizeof x <= 2 * sizeof (hash_hash_t));
-  return (sizeof x == sizeof (hash_hash_t)
+  return 0x1fffffff & (sizeof x == sizeof (hash_hash_t)
 	  ? x
 	  : x ^ (x >> (8 * (sizeof x - sizeof (hash_hash_t)))));
 }