char.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/char.c b/char.c
index 730ae3f5..3706e033 100644
--- a/char.c
+++ b/char.c
@@ -93,6 +93,10 @@ void get_char_constant(struct token *token, unsigned long long *val)
 	if (p != end)
 		warning(token->pos,
 			"multi-character character constant");
+	if (v & 0x80) {
+		if (type >= TOKEN_CHAR && type <= TOKEN_CHAR_EMBEDDED_3)
+			warning(token->pos, "character constant with sign bit set");
+	}
 	*val = v;
 }