diff --git a/src/vim9compile.c b/src/vim9compile.c
index e6c2233..06b6c79 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1802,7 +1802,7 @@
 	    {
 		type = get_type_on_stack(cctx, 1);
 		if (need_type(type, &t_number,
-					    -1, 0, cctx, FALSE, FALSE) == FAIL)
+					    -2, 0, cctx, FALSE, FALSE) == FAIL)
 		return FAIL;
 	    }
 	    type = get_type_on_stack(cctx, 0);