diff --git a/agent/worker/agent_utils.py b/agent/worker/agent_utils.py
index dbc7275..8604d3c 100644
--- a/agent/worker/agent_utils.py
+++ b/agent/worker/agent_utils.py
@@ -399,7 +399,7 @@ def _parse_all_hists(self, hist_paths: List[str]) -> List[str]:
             to_remove = self._parse_and_update_history(hist, to_remove)
         return list(to_remove.keys())
 
-    def _is_base_image(image_name: str):
+    def _is_base_image(self, image_name: str):
         for base_image_name in constants._BASE_IMAGES:
             if image_name.endswith(base_image_name):
                 return True