diff --git a/acconfig.h b/acconfig.h
index eea6cef6db..37401fa379 100644
--- a/acconfig.h
+++ b/acconfig.h
@@ -63,7 +63,7 @@
 #undef HAVE_JPEG            
 
 /* Configure found the function malloc_usable_size */
-#define  HAVE_MALLOC_USABLE_SIZE  
+#undef HAVE_MALLOC_USABLE_SIZE  
 
 /*** Begin i18n ***/