diff --git a/notifications_utils/request_helper.py b/notifications_utils/request_helper.py
index dd0fc0804..dfc4c0c70 100644
--- a/notifications_utils/request_helper.py
+++ b/notifications_utils/request_helper.py
@@ -75,18 +75,13 @@ class ResponseHeaderMiddleware(object):
             if SPAN_ID_HEADER.lower() not in lower_existing_header_names:
                 headers.append((SPAN_ID_HEADER, str(req.span_id)))
 
-            def rewrite_response_headers(status, headers, exc_info=None):
-                lower_existing_header_names = {name.lower() for name, value in headers}
+            # Set COOP once (needed for security)
+            if "cross-origin-opener-policy" not in lower_existing_header_names:
+                headers.append(("Cross-Origin-Opener-Policy", "same-origin"))
 
-                # Set COOP once (needed for security)
-                if "cross-origin-opener-policy" not in lower_existing_header_names:
-                    headers.append(("Cross-Origin-Opener-Policy", "same-origin"))
-
-                # Ensure `Cross-Origin-Resource-Policy: cross-origin` is set
-                if "cross-origin-resource-policy" not in lower_existing_header_names:
-                    headers.append(("Cross-Origin-Resource-Policy", "cross-origin"))
-
-                return start_response(status, headers, exc_info)
+            # Ensure `Cross-Origin-Resource-Policy: cross-origin` is set
+            if "cross-origin-resource-policy" not in lower_existing_header_names:
+                headers.append(("Cross-Origin-Resource-Policy", "cross-origin"))
 
             # svg content type should not contain charset
             found_svg = False