diff --git a/src/main.c b/src/main.c
index a57b196..6d30143 100644
--- a/src/main.c
+++ b/src/main.c
@@ -178,6 +178,8 @@
 #ifdef VIMDLL
     // Check if the current executable file is for the GUI subsystem.
     gui.starting = mch_is_gui_executable();
+#elif defined(FEAT_GUI_MSWIN)
+    gui.starting = TRUE;
 #endif
 
 #ifdef FEAT_CLIENTSERVER
@@ -3242,6 +3244,14 @@
     reset_signals();		/* kill us with CTRL-C here, if you like */
 #endif
 
+    // If this is a Windows GUI executable, show an error dialog box.
+#ifdef VIMDLL
+    gui.in_use = mch_is_gui_executable();
+#endif
+#ifdef FEAT_GUI_MSWIN
+    gui.starting = FALSE;   // Needed to show as error.
+#endif
+
     init_longVersion();
     mch_errmsg(longVersion);
     mch_errmsg("\n");