diff --git a/lib/setup.h b/lib/setup.h
index cdec0f9d66..dc2280da50 100644
--- a/lib/setup.h
+++ b/lib/setup.h
@@ -52,7 +52,7 @@
 #endif
 
 #ifndef __cplusplus        /* (rabe) */
-typedef char bool;
+typedef unsigned char bool;
 #define typedef_bool
 #endif                     /* (rabe) */