diff --git a/library/platform_util.c b/library/platform_util.c
index 756e226..b1f7450 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -72,7 +72,10 @@
 
 void mbedtls_platform_zeroize( void *buf, size_t len )
 {
-    memset_func( buf, 0, len );
+    MBEDTLS_INTERNAL_VALIDATE( len == 0 || buf != NULL );
+
+    if( len > 0 )
+        memset_func( buf, 0, len );
 }
 #endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */