diff --git a/src/structs.h b/src/structs.h
index b5889b7..0715686 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1406,8 +1406,8 @@
 struct type_S {
     vartype_T	    tt_type;
     int8_T	    tt_argcount;    // for func, incl. vararg, -1 for unknown
-    char	    tt_min_argcount; // number of non-optional arguments
-    char	    tt_flags;	    // TTFLAG_ values
+    int8_T	    tt_min_argcount; // number of non-optional arguments
+    char_u	    tt_flags;	    // TTFLAG_ values
     type_T	    *tt_member;	    // for list, dict, func return type
     type_T	    **tt_args;	    // func argument types, allocated
 };