diff --git a/.taskcluster.yml b/.taskcluster.yml
index 6a441c85171..48d0dd60675 100644
--- a/.taskcluster.yml
+++ b/.taskcluster.yml
@@ -44,4 +44,4 @@ tasks:
             git clone $GITHUB_EVENT_CLONE_URL repo &&
             cd repo &&
             git checkout $GITHUB_EVENT_COMMIT_SHA &&
-            python2.7 decision-task.py
+            python3 decision-task.py
diff --git a/decision-task.py b/decision-task.py
index 512e298121e..01dc6d47fbe 100644
--- a/decision-task.py
+++ b/decision-task.py
@@ -16,7 +16,7 @@ def create_task(name, command, artifacts=None, dependencies=None, env=None, cach
     for k in ["GITHUB_EVENT_CLONE_URL", "GITHUB_EVENT_COMMIT_SHA"]:
         env.setdefault(k, os.environ[k])
 
-    task_id = taskcluster.slugId()
+    task_id = taskcluster.slugId().decode("utf8")
     payload = {
         "taskGroupId": decision_task_id,
         "dependencies": [decision_task_id] + (dependencies or []),