diff --git a/lib/tests/scaffold/16-cast.c b/lib/tests/scaffold/16-cast.c
index d83d4e8b..5895a2d7 100644
--- a/lib/tests/scaffold/16-cast.c
+++ b/lib/tests/scaffold/16-cast.c
@@ -21,7 +21,7 @@
 int
 main ()
 {
-  char c = -1;
+  signed char c = -1;
   unsigned u = c;
   unsigned t = (unsigned char)c;
   int i = -1;