diff --git a/include/re_types.h b/include/re_types.h
index 310a869..e0d9e77 100644
--- a/include/re_types.h
+++ b/include/re_types.h
@@ -236,3 +236,13 @@ typedef bool _Bool;
 #ifndef EAUTH
 #define EAUTH 217
 #endif
+
+
+/*
+ * Any C compiler conforming to C99 or later MUST support __func__
+ */
+#if __STDC_VERSION__ >= 199901L
+#define __REFUNC__ (const char *)__func__
+#else
+#define __REFUNC__ __FUNCTION__
+#endif
diff --git a/src/mem/mem.c b/src/mem/mem.c
index 31515d5..1f634c6 100644
--- a/src/mem/mem.c
+++ b/src/mem/mem.c
@@ -104,7 +104,7 @@ static inline void mem_unlock(void)
 #define MAGIC_CHECK(m) \
 	if (mem_magic != (m)->magic) { \
 		DEBUG_WARNING("%s: magic check failed 0x%08x (%p)\n", \
-			      __FUNCTION__, (m)->magic, (m)+1);	      \
+			      __REFUNC__, (m)->magic, (m)+1);	      \
 		BREAKPOINT;					      \
 	}
 #else
diff --git a/src/sys/rand.c b/src/sys/rand.c
index 10df813..f6aa17f 100644
--- a/src/sys/rand.c
+++ b/src/sys/rand.c
@@ -31,7 +31,7 @@ static bool inited = false;
 /** Check random state */
 #define RAND_CHECK							\
 	if (!inited) {							\
-		DEBUG_WARNING("%s: random not inited\n", __FUNCTION__);	\
+		DEBUG_WARNING("%s: random not inited\n", __REFUNC__);	\
 	}
 #else
 #define RAND_CHECK if (0) {}