diff --git a/src/vim9script.c b/src/vim9script.c
index 784283e..7d783ea 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -59,12 +59,29 @@
 }
 
 /*
+ * When in Vim9 script give an error and return FAIL.
+ */
+    int
+not_in_vim9(exarg_T *eap)
+{
+    switch (eap->cmdidx)
+    {
+	case CMD_insert:
+	case CMD_append:
+	case CMD_change:
+	case CMD_xit:
+	    semsg(_("E1100: Missing :let: %s"), eap->cmd);
+	    return FAIL;
+	default: break;
+    }
+    return OK;
+}
+
+/*
  * ":export let Name: type"
  * ":export const Name: type"
  * ":export def Name(..."
  * ":export class Name ..."
- *
- * ":export {Name, ...}"
  */
     void
 ex_export(exarg_T *eap)