diff --git a/src/vim9.h b/src/vim9.h
index 1b5a58b..3ab1c5a 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -296,6 +296,7 @@
     type_T	*ct_type;
     int8_T	ct_off;		// offset in stack, -1 is bottom
     int8_T	ct_arg_idx;	// argument index or zero
+    int8_T	ct_is_var;	// when TRUE checking variable instead of arg
 } checktype_T;
 
 // arguments to ISN_STORENR