diff --git a/src/lisp.h b/src/lisp.h
index a99002bddda..c8363be7a93 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3775,7 +3775,7 @@ INLINE void (check_cons_list) (void) { lisp_h_check_cons_list (); }
 #if !defined DOUG_LEA_MALLOC && !defined HYBRID_MALLOC && !defined SYSTEM_MALLOC
 extern size_t __malloc_extra_blocks;
 #endif
-#ifndef HAVE_DECL_ALIGNED_ALLOC
+#if !HAVE_DECL_ALIGNED_ALLOC
 extern void *aligned_alloc (size_t, size_t) ATTRIBUTE_MALLOC_SIZE ((2));
 #endif
 extern void malloc_enable_thread (void);