diff --git a/src/structs.h b/src/structs.h
index 9f3628e..efc74da 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1342,10 +1342,14 @@
 struct type_S {
     vartype_T	    tt_type;
     short	    tt_argcount;    // for func, partial, -1 for unknown
+    short	    tt_flags;	    // TTFLAG_ values
     type_T	    *tt_member;	    // for list, dict, func return type
-    type_T	    *tt_args;	    // func arguments
+    type_T	    **tt_args;	    // func arguments, allocated
 };
 
+#define TTFLAG_VARARGS	1	    // func args ends with "..."
+#define TTFLAG_OPTARG	2	    // func arg type with "?"
+
 /*
  * Structure to hold an internal variable without a name.
  */