diff --git a/worlds/rogue_legacy/__init__.py b/worlds/rogue_legacy/__init__.py
index eb657699..78e56a79 100644
--- a/worlds/rogue_legacy/__init__.py
+++ b/worlds/rogue_legacy/__init__.py
@@ -49,6 +49,30 @@ class RLWorld(World):
         return {option_name: self.get_setting(option_name).value for option_name in rl_options}
 
     def generate_early(self):
+        location_ids_used_per_game = {
+            world.game: set(world.location_id_to_name) for world in self.multiworld.worlds.values()
+        }
+        item_ids_used_per_game = {
+            world.game: set(world.item_id_to_name) for world in self.multiworld.worlds.values()
+        }
+        overlapping_games = set()
+
+        for id_lookup in (location_ids_used_per_game, item_ids_used_per_game):
+            for game_1, ids_1 in id_lookup.items():
+                for game_2, ids_2 in id_lookup.items():
+                    if game_1 == game_2:
+                        continue
+
+                    if ids_1 & ids_2:
+                        overlapping_games.add(tuple(sorted([game_1, game_2])))
+
+        if overlapping_games:
+            raise RuntimeError(
+                "In this multiworld, there are games with overlapping item/location IDs.\n"
+                "The current Rogue Legacy does not support these and a fix is not currently planned.\n"
+                f"The overlapping games are: {overlapping_games}"
+            )
+        
         # Check validation of names.
         additional_lady_names = len(self.get_setting("additional_lady_names").value)
         additional_sir_names = len(self.get_setting("additional_sir_names").value)