diff --git a/src/aerovaldb/jsondb/jsonfiledb.py b/src/aerovaldb/jsondb/jsonfiledb.py
index f3df9b5..0a456e3 100644
--- a/src/aerovaldb/jsondb/jsonfiledb.py
+++ b/src/aerovaldb/jsondb/jsonfiledb.py
@@ -777,6 +777,10 @@ async def get_map_overlay(
             file_path += ext
             if os.path.exists(file_path):
                 break
+        else:
+            raise FileNotFoundError(
+                f"Overlay for {project}/{experiment}/{source}/{variable}/{date} does not exist."
+            )
 
         logger.debug(f"Fetching image with path '{file_path}'")