diff --git a/beets/util/__init__.py b/beets/util/__init__.py
index bb84aedc7..cc23b6874 100644
--- a/beets/util/__init__.py
+++ b/beets/util/__init__.py
@@ -227,6 +227,8 @@ def path_as_posix(path):
     """Return the string representation of the path with forward (/)
     slashes.
     """
+    if isinstance(path, str):
+        return path.replace('\\', '/')
     return path.replace(b'\\', b'/')