diff --git a/ext/standard/string.c b/ext/standard/string.c
index f3f78100b4c6f..bc610659e5ac1 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -280,6 +280,7 @@ PHP_FUNCTION(hex2bin)
 	result = php_hex2bin((unsigned char *)data, datalen, &newlen);
 
 	if (!result) {
+		php_error_docref(NULL TSRMLS_CC, E_WARNING, "Input string must be hexadecimal string");
 		RETURN_FALSE;
 	}