1 files changed, 12 insertions, 0 deletions
diff --git a/src/doom/d_main.c b/src/doom/d_main.c
index 95342437..70144fb6 100644
--- a/src/doom/d_main.c
+++ b/src/doom/d_main.c
@@ -1387,6 +1387,18 @@ void D_DoomMain (void)
     I_PrintStartupBanner(gamedescription);
     PrintDehackedBanners();
 
+    // Freedoom's IWADs are Boom-compatible, which means they usually
+    // don't work in Vanilla (though FreeDM is okay). Show a warning
+    // message and give a link to the website.
+    if (W_CheckNumForName("FREEDOOM") >= 0 && W_CheckNumForName("FREEDM") < 0)
+    {
+        printf(" WARNING: You are playing using one of the Freedoom IWAD\n"
+               " files, which might not work in this port. See this page\n"
+               " for more information on how to play using Freedoom:\n"
+               "   http://www.chocolate-doom.org/wiki/index.php/Freedoom\n");
+        I_PrintDivider();
+    }
+
     DEH_printf("I_Init: Setting up machine state.\n");
     I_CheckIsScreensaver();
     I_InitTimer();