diff --git a/include/cstdlib b/include/cstdlib
index c817fd8..25a829b 100644
--- a/include/cstdlib
+++ b/include/cstdlib
@@ -141,11 +141,11 @@ using ::wctomb _LIBCPP_USING_IF_EXISTS;
 using ::mbstowcs _LIBCPP_USING_IF_EXISTS;
 using ::wcstombs _LIBCPP_USING_IF_EXISTS;
 #endif
-#if !defined(_LIBCPP_CXX03_LANG)
+#if !defined(_LIBCPP_CXX03_LANG) && __has_attribute(using_if_exists)
 using ::at_quick_exit _LIBCPP_USING_IF_EXISTS;
 using ::quick_exit _LIBCPP_USING_IF_EXISTS;
 #endif
-#if _LIBCPP_STD_VER >= 17
+#if _LIBCPP_STD_VER >= 17 && __has_attribute(using_if_exists) && !defined(_LIBCPP_MSVCRT)
 using ::aligned_alloc _LIBCPP_USING_IF_EXISTS;
 #endif
 
diff --git a/include/ctime b/include/ctime
index f47b49a..cad942e 100644
--- a/include/ctime
+++ b/include/ctime
@@ -65,7 +65,7 @@ using ::clock_t _LIBCPP_USING_IF_EXISTS;
 using ::size_t _LIBCPP_USING_IF_EXISTS;
 using ::time_t _LIBCPP_USING_IF_EXISTS;
 using ::tm _LIBCPP_USING_IF_EXISTS;
-#if _LIBCPP_STD_VER >= 17
+#if _LIBCPP_STD_VER >= 17 && __has_attribute(using_if_exists)
 using ::timespec _LIBCPP_USING_IF_EXISTS;
 #endif
 using ::clock _LIBCPP_USING_IF_EXISTS;
@@ -77,7 +77,7 @@ using ::ctime _LIBCPP_USING_IF_EXISTS;
 using ::gmtime _LIBCPP_USING_IF_EXISTS;
 using ::localtime _LIBCPP_USING_IF_EXISTS;
 using ::strftime _LIBCPP_USING_IF_EXISTS;
-#if _LIBCPP_STD_VER >= 17
+#if _LIBCPP_STD_VER >= 17 && __has_attribute(using_if_exists)
 using ::timespec_get _LIBCPP_USING_IF_EXISTS;
 #endif