diff --git a/truss/contexts/image_builder/serving_image_builder.py b/truss/contexts/image_builder/serving_image_builder.py
index 5a38aacaf..73916e9a0 100644
--- a/truss/contexts/image_builder/serving_image_builder.py
+++ b/truss/contexts/image_builder/serving_image_builder.py
@@ -158,7 +158,11 @@ def list_files(self, revision=None):
 
         all_objects = []
         for blob in bucket.objects.filter(Prefix=path):
+            # leave out folders
+            if blob.key[-1] == "/":
+                continue
             all_objects.append(blob.key)
+
         return all_objects
 
     def prepare_for_cache(self, filenames):