diff --git a/include/__config b/include/__config
index e49adb4..f1b7390 100644
--- a/include/__config
+++ b/include/__config
@@ -183,10 +183,6 @@
 #  define _LIBCPP_COMPILER_IBM
 #endif
 
-#ifndef _LIBCPP_CLANG_VER
-#define _LIBCPP_CLANG_VER 0
-#endif
-
 #if defined(_LIBCPP_COMPILER_GCC) && __cplusplus < 201103L
 #error "libc++ does not support using GCC with C++03. Please enable C++11"
 #endif
@@ -484,7 +480,7 @@
 #define _LIBCPP_ALWAYS_INLINE __attribute__ ((__always_inline__))
 
 // No apple compilers support ""d and ""y at this time.
-#if _LIBCPP_CLANG_VER < 800 || defined(__apple_build_version__)
+#if (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER < 800) || defined(__apple_build_version__)
 #define	_LIBCPP_HAS_NO_CXX20_CHRONO_LITERALS
 #endif
 
@@ -1242,7 +1238,7 @@
 
 #ifndef _LIBCPP_NODEBUG_TYPE
 #if __has_attribute(__nodebug__) && \
-    (defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER >= 900)
+    (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 900)
 #define _LIBCPP_NODEBUG_TYPE __attribute__((nodebug))
 #else
 #define _LIBCPP_NODEBUG_TYPE