diff --git a/beetsplug/convert.py b/beetsplug/convert.py
index fc9e368fa..c46b2fc85 100644
--- a/beetsplug/convert.py
+++ b/beetsplug/convert.py
@@ -49,8 +49,6 @@ def replace_ext(path, ext):
 
     The new extension must not contain a leading dot.
     """
-    assert isinstance(path, bytes)
-    assert isinstance(ext, bytes)
     ext_dot = b"." + ext
     return os.path.splitext(path)[0] + ext_dot