diff --git a/src/test/locale/test-ctype.c b/src/test/locale/test-ctype.c
index 93358bf9de4a8579be34f826f630a9b9f332da82..8cf5e17da7f9ddd946003a597396cab0c692c03f 100644
--- a/src/test/locale/test-ctype.c
+++ b/src/test/locale/test-ctype.c
@@ -39,7 +39,7 @@ flag(int b)
 void
 describe_char(int c)
 {
-	char		cp = c,
+	unsigned char		cp = c,
 				up = toupper(c),
 				lo = tolower(c);