diff --git a/mysys/mf_keycache.c b/mysys/mf_keycache.c
index 6ffa8fb3ea8..53a3be6f999 100644
--- a/mysys/mf_keycache.c
+++ b/mysys/mf_keycache.c
@@ -1742,7 +1742,7 @@ restart:
       - block assigned but not yet read from file (invalid data).
   */
 
-#if THREAD
+#ifdef THREAD
   if (keycache->in_resize)
   {
     /* This is a request during a resize operation */