diff --git a/src/option.c b/src/option.c
index ae30310..90e3e6d 100644
--- a/src/option.c
+++ b/src/option.c
@@ -1230,9 +1230,10 @@
  */
     int
 do_set(
-    char_u	*arg,		// option string (may be written to!)
+    char_u	*arg_start,	// option string (may be written to!)
     int		opt_flags)
 {
+    char_u	*arg = arg_start;
     int		opt_idx;
     char	*errmsg;
     char	errbuf[80];
@@ -1387,7 +1388,11 @@
 
 	    if (opt_idx == -1 && key == 0)	// found a mismatch: skip
 	    {
-		errmsg = N_("E518: Unknown option");
+		if (in_vim9script() && arg > arg_start
+				  && vim_strchr((char_u *)"!&<", *arg) != NULL)
+		    errmsg = e_no_white_space_allowed_between_option_and;
+		else
+		    errmsg = N_("E518: Unknown option");
 		goto skip;
 	    }