diff --git a/agasc/agasc.py b/agasc/agasc.py
index 9bd5d64d..b6ee6c9d 100644
--- a/agasc/agasc.py
+++ b/agasc/agasc.py
@@ -296,7 +296,9 @@ def get_agasc_filename(
     """
     if agasc_file is None:
         if "AGASC_HDF5_FILE" in os.environ:
-            return str(default_agasc_dir() / os.environ["AGASC_HDF5_FILE"])
+            agasc_file = os.environ["AGASC_HDF5_FILE"]
+            if agasc_file.endswith(".h5"):
+                return str(default_agasc_dir() / os.environ["AGASC_HDF5_FILE"])
         else:
             agasc_file = "proseco_agasc_*"