diff --git a/src/d_netcmd.c b/src/d_netcmd.c
index 6e798af1e..2c76b7581 100644
--- a/src/d_netcmd.c
+++ b/src/d_netcmd.c
@@ -2862,6 +2862,15 @@ static void Command_Map_f(void)
 	// G_TOLFlag handles both multiplayer gametype and ignores it for !multiplayer
 	else
 	{
+		
+		if (!mapheaderinfo[newmapnum-1] || mapheaderinfo[newmapnum-1] == NULL)
+		{
+			CONS_Alert(CONS_WARNING, M_GetText("Invalid mapheaderinfo for Course %s (%s)\n"), realmapname, G_BuildMapName(newmapnum));
+			Z_Free(realmapname);
+			Z_Free(mapname);
+			return;
+		}
+		
 		if (!(
 					mapheaderinfo[newmapnum-1] &&
 					mapheaderinfo[newmapnum-1]->typeoflevel & G_TOLFlag(newgametype)