diff --git a/runtime/doc/gui_mac.txt b/runtime/doc/gui_mac.txt
index 6848413850..ce06b548c4 100644
--- a/runtime/doc/gui_mac.txt
+++ b/runtime/doc/gui_mac.txt
@@ -108,6 +108,10 @@ guitablabel=" to your .gvimrc file to revert back to the default Vim tab
 label.  Setting 'guitablabel' to anything in your .vimrc will also prevent
 this default from taking effect.
 
+							*E9000-M*
+Below is a list of non-standard Vim commands and options that MacVim supports.
+They are only usable when GUI is active.
+
 							*macvim-options*
 These are the non-standard options that MacVim supports:
 	'antialias'	'blurradius'	'fullscreen'
@@ -503,7 +507,7 @@ file for more examples on how to set up menus.  Note: When no window is open a
 minimal default menu is used.  The default menu is set up in MainMenu.nib
 which resides in "Resources/English.lproj/" folder inside the app bundle.
 
-							*Actions.plist*
+							*E9001-M* *Actions.plist*
 Some action messages would not be suitable to call from within Vim, so there
 is a dictionary called "Actions.plist" (in the Resources folder of the
 application bundle) which contains all actions that may be called.  The key in
diff --git a/runtime/doc/tags b/runtime/doc/tags
index 2ab81d4dde..06ddf5c301 100644
--- a/runtime/doc/tags
+++ b/runtime/doc/tags
@@ -5226,6 +5226,8 @@ E898	channel.txt	/*E898*
 E899	eval.txt	/*E899*
 E90	message.txt	/*E90*
 E900	builtin.txt	/*E900*
+E9000-M	gui_mac.txt	/*E9000-M*
+E9001-M	gui_mac.txt	/*E9001-M*
 E901	channel.txt	/*E901*
 E902	channel.txt	/*E902*
 E903	channel.txt	/*E903*
diff --git a/runtime/menu.vim b/runtime/menu.vim
index 4d3756c049..9367e4f8c1 100644
--- a/runtime/menu.vim
+++ b/runtime/menu.vim
@@ -1012,7 +1012,7 @@ endif " !has("gui_macvim")
 " The popup menu
 if has("gui_macvim")
   vnoremenu 1.05 PopUp.Look\ Up     :<C-U>call macvim#ShowDefinitionSelected()<CR>
-  vnoremenu 1.06 PopUp.-SEP10-      <Nop>
+  vnoremenu 1.06 PopUp.-SEPLookUp-      <Nop>
 endif
 
 an 1.10 PopUp.&Undo			u
diff --git a/src/MacVim/gui_macvim.m b/src/MacVim/gui_macvim.m
index e34a2dfe3b..8c675f58cb 100644
--- a/src/MacVim/gui_macvim.m
+++ b/src/MacVim/gui_macvim.m
@@ -1461,7 +1461,7 @@
     exarg_T	*eap;
 {
     if (!gui.in_use) {
-        emsg(_("E???: Command only available in GUI mode"));
+        emsg(_("E9000-M: Command only available in GUI mode"));
         return;
     }
 
@@ -1473,7 +1473,7 @@
     if (actionDict && [actionDict objectForKey:name] != nil) {
         [[MMBackend sharedInstance] executeActionWithName:name];
     } else {
-        semsg(_("E???: Invalid action: %s"), eap->arg);
+        semsg(_("E9001-M: Invalid action: %s"), eap->arg);
     }
 
     arg = CONVERT_TO_UTF8(arg);
@@ -2540,6 +2540,11 @@
 /// Implementation of showdefinition()
 void f_showdefinition(typval_T *argvars, typval_T *rettv UNUSED)
 {
+    if (!gui.in_use) {
+        emsg(_("E9000-M: Command only available in GUI mode"));
+        return;
+    }
+
     if (in_vim9script() && check_for_string_arg(argvars, 0) == FAIL)
 	return;
 
diff --git a/src/menu.c b/src/menu.c
index 2a4916b50b..3cd7408e96 100644
--- a/src/menu.c
+++ b/src/menu.c
@@ -3041,7 +3041,7 @@ ex_macmenu(exarg_T *eap)
 
 	    if (!is_valid_macaction(action))
 	    {
-		semsg(_("E???: Invalid action: %s"), arg);
+		semsg(_("E9001-M: Invalid action: %s"), arg);
 		error = TRUE;
 		break;
 	    }
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index f28efc9257..259460086b 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -891,6 +891,11 @@ func Test_popup_command()
   call writefile(lines, 'Xtest', 'D')
   let buf = RunVimInTerminal('-S XtimerScript Xtest', {})
   call term_sendkeys(buf, ":source $VIMRUNTIME/menu.vim\<CR>")
+  if has('gui_macvim')
+    " Remove the non-standard MacVim menus to the navigation below will work.
+    call term_sendkeys(buf, ":aunmenu PopUp.Look\\ Up\<CR>")
+    call term_sendkeys(buf, ":aunmenu PopUp.-SEPLookUp-\<CR>")
+  endif
   call term_sendkeys(buf, "/X\<CR>:popup PopUp\<CR>")
   call VerifyScreenDump(buf, 'Test_popup_command_01', {})