diff --git a/bumpversion/__init__.py b/bumpversion/__init__.py
index a4af337..69a34d4 100644
--- a/bumpversion/__init__.py
+++ b/bumpversion/__init__.py
@@ -72,7 +72,7 @@ def commit(cls, message):
         f.write(message.encode('utf-8'))
         f.close()
         subprocess.check_output(cls._COMMIT_COMMAND + [f.name], env=dict(
-            list(os.environ.items()) + [(b'HGENCODING', b'utf-8')]
+            list(os.environ.items()) + [(str('HGENCODING'), str('utf-8'))]
         ))
         os.unlink(f.name)
 
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 7067472..6cde128 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -21,7 +21,7 @@
     split_args_in_optional_and_positional
 
 SUBPROCESS_ENV = dict(
-    list(environ.items()) + [(b'HGENCODING', b'utf-8')]
+    list(environ.items()) + [(str('HGENCODING'), str('utf-8'))]
 )
 
 call = partial(subprocess.call, env=SUBPROCESS_ENV)