--- a/devtools/server/tests/browser/browser_animation_keepFinished.js
+++ b/devtools/server/tests/browser/browser_animation_keepFinished.js
@@ -30,16 +30,19 @@ add_task(function*() {
   info("Add a short animation on the node");
   yield node.modifyAttributes([
     {attributeName: "class", newValue: "short-animation"}
   ]);
 
   info("Wait for longer than the animation's duration");
   yield wait(2000);
 
+  players = yield animations.getAnimationPlayersForNode(node);
+  is(players.length, 0, "The added animation is surely finished");
+
   is(reportedMutations.length, 1, "Only one mutation was reported");
   is(reportedMutations[0].type, "added", "The mutation was an addition");
 
   animations.off("mutations", onMutations);
 
   yield closeDebuggerClient(client);
   gBrowser.removeCurrentTab();
 });