diff --git a/src/vim9cmds.c b/src/vim9cmds.c
index 6d8935a..5c7a938 100644
--- a/src/vim9cmds.c
+++ b/src/vim9cmds.c
@@ -843,8 +843,11 @@
 	// If we know the type of "var" and it is a not a supported type we can
 	// give an error now.
 	vartype = ((type_T **)stack->ga_data)[stack->ga_len - 1];
-	if (vartype->tt_type != VAR_LIST && vartype->tt_type != VAR_STRING
-		&& vartype->tt_type != VAR_BLOB && vartype->tt_type != VAR_ANY)
+	if (vartype->tt_type != VAR_LIST
+		&& vartype->tt_type != VAR_STRING
+		&& vartype->tt_type != VAR_BLOB
+		&& vartype->tt_type != VAR_ANY
+		&& vartype->tt_type != VAR_UNKNOWN)
 	{
 	    semsg(_(e_for_loop_on_str_not_supported),
 					       vartype_name(vartype->tt_type));