--- a/taskcluster/taskgraph/task/legacy.py
+++ b/taskcluster/taskgraph/task/legacy.py
@@ -174,21 +174,22 @@ def remove_coalescing_from_task(task):
     :param task: task definition.
     """
     patterns = [
         re.compile("^coalesce.v1.builds.*pgo$"),
     ]
 
     try:
         payload = task["task"]["payload"]
-        payload.pop("supersederUrl")
-
         routes = task["task"]["routes"]
         removable_routes = [route for route in list(routes)
                             if any([p.match(route) for p in patterns])]
+        if removable_routes:
+            # we remove supersederUrl only when we have also routes to remove
+            payload.pop("supersederUrl")
 
         for route in removable_routes:
             routes.remove(route)
     except KeyError:
         pass
 
 
 def query_vcs_info(repository, revision):