diff --git a/edosl0util/stream.py b/edosl0util/stream.py
index e06237f2ca4574de97cffcee1e7d95fee82cea38..1f90377b9bb8f742de31fe699af60cda8aa9436d 100644
--- a/edosl0util/stream.py
+++ b/edosl0util/stream.py
@@ -71,6 +71,8 @@ class SequenceId(object):
 
 
 def default_header_lookup(primary_header):
+    if not primary_header.secondary_header_flag:
+        return None
     return (
         headers.aqua_header_lookup(primary_header) or
         headers.jpss_header_lookup(primary_header)