diff --git a/blender_asset_tracer/pack/__init__.py b/blender_asset_tracer/pack/__init__.py
index 72980b6..3a60bc4 100644
--- a/blender_asset_tracer/pack/__init__.py
+++ b/blender_asset_tracer/pack/__init__.py
@@ -475,7 +475,8 @@ class Packer:
             # It is *not* used for any disk I/O, since the file may not even
             # exist on the local filesystem.
             bfile_pp = action.new_path
-            assert bfile_pp is not None
+            assert bfile_pp is not None, \
+                f"Action {action.path_action.name} on {bfile_path} has no final path set, unable to process"
 
             # Use tempfile to create a unique name in our temporary directoy.
             # The file should be deleted when self.close() is called, and not