diff --git a/cellxgene_gateway/dir_util.py b/cellxgene_gateway/dir_util.py
index 3ca9957..84aa9b0 100644
--- a/cellxgene_gateway/dir_util.py
+++ b/cellxgene_gateway/dir_util.py
@@ -62,3 +62,8 @@ def make_h5ad(el):
 
 def make_annotations(el):
     return el[:-5] + annotations_suffix
+
+
+def ensure_dir_exists(file_path):
+    if not os.path.exists(file_path):
+        os.makedirs(file_path)
diff --git a/cellxgene_gateway/items/file/fileitem_source.py b/cellxgene_gateway/items/file/fileitem_source.py
index d7e44f5..073425c 100644
--- a/cellxgene_gateway/items/file/fileitem_source.py
+++ b/cellxgene_gateway/items/file/fileitem_source.py
@@ -130,6 +130,7 @@ class FileItemSource(ItemSource):
             )
             item = self.lookup_item(h5ad_descriptor)
             if item is not None:
+                dir_util.ensure_dir_exists(self.full_path(annotation_item.subpath))
                 return LookupResult(item, annotation_item)
         else:
             item = self.lookup_item(descriptor)