diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 9b6da31..92035d4 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -79,7 +79,7 @@
 #define	___STRING(x)	__STRING(x)
 #define	___CONCAT(x,y)	__CONCAT(x,y)
 
-#if __STDC__ || defined(__cplusplus)
+#if defined(__STDC__) || defined(__cplusplus)
 #define	__P(protos)	protos		/* full-blown ANSI C */
 #define	__CONCAT(x,y)	x ## y
 #define	__STRING(x)	#x
@@ -213,7 +213,7 @@
  * C99 defines the restrict type qualifier keyword, which was made available
  * in GCC 2.92.
  */
-#if __STDC_VERSION__ >= 199901L
+#if defined(__STDC__VERSION__) && __STDC_VERSION__ >= 199901L
 #define	__restrict	restrict
 #else
 #if !__GNUC_PREREQ__(2, 92)
@@ -225,7 +225,7 @@
  * C99 defines __func__ predefined identifier, which was made available
  * in GCC 2.95.
  */
-#if !(__STDC_VERSION__ >= 199901L)
+#if !defined(__STDC_VERSION__) || !(__STDC_VERSION__ >= 199901L)
 #if __GNUC_PREREQ__(2, 6)
 #define	__func__	__PRETTY_FUNCTION__
 #elif __GNUC_PREREQ__(2, 4)