diff --git a/include/type_traits b/include/type_traits
index 6461151..e1cd1e1 100644
--- a/include/type_traits
+++ b/include/type_traits
@@ -709,7 +709,7 @@
 
 // is_base_of
 
-#ifdef __has_feature(is_base_of)
+#if __has_feature(is_base_of)
 
 template <class _Bp, class _Dp>
 struct _LIBCPP_VISIBLE is_base_of