diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index e82e91b..7888d6f 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -741,7 +741,7 @@
 	EX_TRLBAR|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_NONE),
 EXCMD(CMD_k,		"k",		ex_mark,
-	EX_RANGE|EX_WORD1|EX_TRLBAR|EX_SBOXOK|EX_CMDWIN|EX_LOCK_OK,
+	EX_RANGE|EX_WORD1|EX_TRLBAR|EX_SBOXOK|EX_CMDWIN|EX_LOCK_OK|EX_NONWHITE_OK,
 	ADDR_LINES),
 EXCMD(CMD_keepmarks,	"keepmarks",	ex_wrongmodifier,
 	EX_NEEDARG|EX_EXTRA|EX_NOTRLCOM,
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 371f3d6..77162ec 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3461,7 +3461,8 @@
     /*
      * Isolate the command and search for it in the command table.
      * Exceptions:
-     * - the 'k' command can directly be followed by any character.
+     * - The 'k' command can directly be followed by any character.
+     *   But it is not used in Vim9 script.
      * - the 's' command can be followed directly by 'c', 'g', 'i', 'I' or 'r'
      *	    but :sre[wind] is another command, as are :scr[iptnames],
      *	    :scs[cope], :sim[alt], :sig[ns] and :sil[ent].
@@ -8056,6 +8057,10 @@
 {
     pos_T	pos;
 
+#ifdef FEAT_EVAL
+    if (not_in_vim9(eap) == FAIL)
+	return;
+#endif
     if (*eap->arg == NUL)		// No argument?
 	emsg(_(e_argreq));
     else if (eap->arg[1] != NUL)	// more than one character?
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index f444bb5..d22c653 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -3491,6 +3491,31 @@
   unlet g:guard
 enddef
 
+def Test_unsupported_commands()
+  var lines =<< trim END
+      ka
+  END
+  CheckDefAndScriptFailure(lines, 'E1100:')
+
+  lines =<< trim END
+    t
+  END
+  CheckDefFailure(lines, 'E1100:')
+  CheckScriptFailure(['vim9script'] + lines, 'E1100:')
+
+  lines =<< trim END
+    x
+  END
+  CheckDefFailure(lines, 'E1100:')
+  CheckScriptFailure(['vim9script'] + lines, 'E1100:')
+
+  lines =<< trim END
+    xit
+  END
+  CheckDefFailure(lines, 'E1100:')
+  CheckScriptFailure(['vim9script'] + lines, 'E1100:')
+enddef
+
 " Keep this last, it messes up highlighting.
 def Test_substitute_cmd()
   new
diff --git a/src/version.c b/src/version.c
index 7e42fa3..d802a49 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2531,
+/**/
     2530,
 /**/
     2529,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 84c9108..c75ead9 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -8520,6 +8520,7 @@
 	    case CMD_append:
 	    case CMD_change:
 	    case CMD_insert:
+	    case CMD_k:
 	    case CMD_t:
 	    case CMD_xit:
 		    not_in_vim9(&ea);
diff --git a/src/vim9script.c b/src/vim9script.c
index d40104c..751d8fb 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -95,6 +95,7 @@
 	    case CMD_append:
 	    case CMD_change:
 	    case CMD_insert:
+	    case CMD_k:
 	    case CMD_t:
 	    case CMD_xit:
 		semsg(_(e_command_not_supported_in_vim9_script_missing_var_str), eap->cmd);