diff --git a/ext/standard/math.c b/ext/standard/math.c
index 734ebaba075..0cd7ecfbb57 100644
--- a/ext/standard/math.c
+++ b/ext/standard/math.c
@@ -159,6 +159,8 @@ static inline double php_round_helper(double value, int mode) {
 			return integral;
 		EMPTY_SWITCH_DEFAULT_CASE();
 	}
+	// FIXME: GCC bug, branch is considered reachable.
+	ZEND_UNREACHABLE();
 }
 /* }}} */