diff --git a/tools/UpdatePaths/__main__.py b/tools/UpdatePaths/__main__.py
index 8ce7a3a92ca..804f34c88c0 100644
--- a/tools/UpdatePaths/__main__.py
+++ b/tools/UpdatePaths/__main__.py
@@ -138,20 +138,25 @@ def update_path(dmm_data, replacement_string, verbose=False):
             return [element]
 
     bad_keys = {}
+    modified_keys = []
     keys = list(dmm_data.dictionary.keys())
     for definition_key in keys:
         def_value = dmm_data.dictionary[definition_key]
         new_value = tuple(y for x in def_value for y in get_result(x) if y != None)
         if new_value != def_value:
             dmm_data.overwrite_key(definition_key, new_value, bad_keys)
+            modified_keys.append(definition_key)
     dmm_data.reassign_bad_keys(bad_keys)
+    return modified_keys
 
 
 def update_map(map_filepath, updates, verbose=False):
     print("Updating: {0}".format(map_filepath))
     dmm_data = DMM.from_file(map_filepath)
+    modified_keys = []
     for update_string in updates:
-        update_path(dmm_data, update_string, verbose)
+        modified_keys.extend(update_path(dmm_data, update_string, verbose))
+    dmm_data.remove_unused_keys(modified_keys)
     dmm_data.to_file(map_filepath)
 
 
diff --git a/tools/mapmerge2/dmm.py b/tools/mapmerge2/dmm.py
index 453cdf5c8af..cd6869d4c1e 100644
--- a/tools/mapmerge2/dmm.py
+++ b/tools/mapmerge2/dmm.py
@@ -83,6 +83,14 @@ class DMM:
             # reassign the grid entries which used the old key
             self.grid[k] = bad_keys.get(v, v)
 
+    def remove_unused_keys(self, modified_keys = None):
+        unused_keys = modified_keys if modified_keys is not None else self.dictionary.keys()
+        for key in self.grid.values():
+            if key in unused_keys:
+                unused_keys.remove(key)
+        for key in unused_keys:
+            del self.dictionary[key]
+
     def _presave_checks(self):
         # last-second handling of bogus keys to help prevent and fix broken maps
         self._ensure_free_keys(0)