diff --git a/devtools/client/aboutdebugging/test/browser_service_workers_start.js b/devtools/client/aboutdebugging/test/browser_service_workers_start.js
index 7dbe571e15bc..0bb9f052dcf3 100644
--- a/devtools/client/aboutdebugging/test/browser_service_workers_start.js
+++ b/devtools/client/aboutdebugging/test/browser_service_workers_start.js
@@ -55,12 +55,18 @@ add_task(function* () {
   ok(name, "Found the service worker in the list");
   let targetElement = name.parentNode.parentNode;
 
-  // Check that there is a Debug button but not a Start button.
-  ok(targetElement.querySelector(".debug-button"), "Found its debug button");
-  ok(!targetElement.querySelector(".start-button"), "No start button");
+  // The service worker may already be killed with the low 1s timeout
+  if (!targetElement.querySelector(".start-button")) {
+    // Check that there is a Debug button but not a Start button.
+    ok(targetElement.querySelector(".debug-button"), "Found its debug button");
 
-  // Wait for the service worker to be killed due to inactivity.
-  yield waitForMutation(targetElement, { childList: true });
+    // Wait for the service worker to be killed due to inactivity.
+    yield waitForMutation(targetElement, { childList: true });
+  } else {
+    // Check that there is no Debug button when the SW is already shut down.
+    ok(!targetElement.querySelector(".debug-button"), "No debug button when " +
+      "the worker is already killed");
+  }
 
   // We should now have a Start button but no Debug button.
   let startBtn = targetElement.querySelector(".start-button");