diff --git a/toolkit/devtools/server/actors/animation.js b/toolkit/devtools/server/actors/animation.js
index 12d468e10014..d1a4de6e0361 100644
--- a/toolkit/devtools/server/actors/animation.js
+++ b/toolkit/devtools/server/actors/animation.js
@@ -483,7 +483,17 @@ let AnimationPlayerFront = FrontClass(AnimationPlayerActor, {
       return;
     }
 
-    this.autoRefreshTimer = setInterval(this.refreshState.bind(this), interval);
+    this.autoRefreshTimer = setInterval(() => {
+      // Save the refresh promise for tests. The tests need to detect when the
+      // last request completes or they might finish too early.
+      // Storing the latest Promise is enough to know that there is no pending
+      // requests left as p.js guarantees the last request will get the reply
+      // last.
+      this.pendingRefreshStatePromise = this.refreshState();
+      this.pendingRefreshStatePromise.then(() => {
+        this.pendingRefreshStatePromise = null;
+      });
+    }, interval);
   },
 
   /**
diff --git a/toolkit/devtools/server/tests/browser/browser_animation_actors_05.js b/toolkit/devtools/server/tests/browser/browser_animation_actors_05.js
index 8fceb167b257..515b4b9adf4c 100644
--- a/toolkit/devtools/server/tests/browser/browser_animation_actors_05.js
+++ b/toolkit/devtools/server/tests/browser/browser_animation_actors_05.js
@@ -45,7 +45,13 @@ add_task(function*() {
         info("Stop the auto-refresh");
         player.stopAutoRefresh();
 
-        resolve();
+        if (player.pendingRefreshStatePromise) {
+          // A new request was fired before we had chance to stop it. Wait for
+          // it to complete.
+          player.pendingRefreshStatePromise.then(resolve);
+        } else {
+          resolve();
+        }
       }
     };
     player.on(player.AUTO_REFRESH_EVENT, onNewState);