diff --git a/src/include/c.h b/src/include/c.h
index 3ea748ff58..658be50e0d 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -305,7 +305,7 @@
 #else
 
 #ifndef bool
-typedef char bool;
+typedef unsigned char bool;
 #endif
 
 #ifndef true