diff --git a/bin/key-mapper-gtk b/bin/key-mapper-gtk
index 49629d81..9b5ad444 100755
--- a/bin/key-mapper-gtk
+++ b/bin/key-mapper-gtk
@@ -438,6 +438,8 @@ if __name__ == '__main__':
     log_info()
 
     if getpass.getuser() != 'root' and 'unittest' not in sys.modules.keys():
+        # TODO
+        # add a polkit thing like https://gitlab.manjaro.org/applications/pamac/-/tree/master/data/polkit
         logger.error('Needs to run with sudo')
         ErrorDialog(
             'Error',
diff --git a/keymapper/X.py b/keymapper/X.py
index 6787ab37..70fd9e83 100644
--- a/keymapper/X.py
+++ b/keymapper/X.py
@@ -99,6 +99,19 @@ class Mapping:
         new_keycode : int
         character : string
         """
+        try:
+            new_keycode = int(new_keycode)
+        except ValueError:
+            logger.error('Cannot use %s as keycode', new_keycode)
+            return False
+
+        if previous_keycode is not None:
+            try:
+                previous_keycode = int(previous_keycode)
+            except ValueError:
+                logger.error('Cannot use %s as keycode', previous_keycode)
+                return False
+
         if new_keycode and character:
             self._mapping[new_keycode] = str(character)
             if new_keycode != previous_keycode:
@@ -106,7 +119,9 @@ class Mapping:
                 # representing that one will now represent a different one.
                 self.clear(previous_keycode)
             self.changed = True
-        return self.changed
+            return True
+
+        return False
 
     def clear(self, keycode):
         """Remove a keycode from the mapping.
diff --git a/keymapper/paths.py b/keymapper/paths.py
index a955d377..77f54bf7 100644
--- a/keymapper/paths.py
+++ b/keymapper/paths.py
@@ -28,7 +28,8 @@ Is a module so that tests can modify them.
 import os
 
 
-# the path in home, is symlinked with SYMBOLS_PATH
+# the path in home, is symlinked with SYMBOLS_PATH.
+# getlogin gets the user who ran sudo
 CONFIG_PATH = os.path.join('/home', os.getlogin(), '.config/key-mapper')
 
 # should not contain spaces
diff --git a/tests/testcases/mapping.py b/tests/testcases/mapping.py
index 40de4a6d..ea0d31a5 100644
--- a/tests/testcases/mapping.py
+++ b/tests/testcases/mapping.py
@@ -59,6 +59,15 @@ class TestMapping(unittest.TestCase):
         self.assertEqual(self.mapping.get(4), 'e')
         self.assertEqual(len(self.mapping), 2)
 
+        # and this
+        self.mapping.change('4', '4', 'f')
+        self.assertEqual(self.mapping.get(4), 'f')
+        self.assertEqual(len(self.mapping), 2)
+
+        # non-ints are ignored
+        self.mapping.change('a', 'b', 'c')
+        self.assertEqual(len(self.mapping), 2)
+
     def test_clear(self):
         # does nothing
         self.mapping.clear(40)