diff --git a/allensdk/brain_observatory/ecephys/ecephys_session_api/ecephys_nwb1_session_api.py b/allensdk/brain_observatory/ecephys/ecephys_session_api/ecephys_nwb1_session_api.py
index e1b9a7d95..4e94fbed4 100644
--- a/allensdk/brain_observatory/ecephys/ecephys_session_api/ecephys_nwb1_session_api.py
+++ b/allensdk/brain_observatory/ecephys/ecephys_session_api/ecephys_nwb1_session_api.py
@@ -62,8 +62,10 @@ def __init__(self, path, *args, **kwargs):
         try:
             # check file is a valid NWB 1 file
             version_str = self._h5_root['nwb_version'][()]
-            if not (version_str.startswith(b'NWB-1.') or
-                    version_str.startswith(b'1.')):
+            if isinstance(version_str, bytes):
+                version_str = version_str.decode('utf-8')
+            if not (version_str.startswith('NWB-1.') or
+                    version_str.startswith('1.')):
                 raise Exception(
                     '{} is not a valid NWB 1 file path'.format(self._path))
         except Exception: