--- a/dom/animation/AnimationPlayer.cpp
+++ b/dom/animation/AnimationPlayer.cpp
@@ -420,37 +420,45 @@ AnimationPlayer::ComposeStyle(nsRefPtr<c
 
 void
 AnimationPlayer::DoPlay()
 {
   // FIXME: When we implement finishing behavior (bug 1074630) we will
   // need to pass a flag so that when we start playing due to a change in
   // animation-play-state we *don't* trigger finishing behavior.
 
+  bool reuseReadyPromise = false;
+  if (mPendingState != PendingState::NotPending) {
+    CancelPendingTasks();
+    reuseReadyPromise = true;
+  }
+
   Nullable<TimeDuration> currentTime = GetCurrentTime();
   if (mPlaybackRate > 0.0 &&
       (currentTime.IsNull())) {
     mHoldTime.SetValue(TimeDuration(0));
   } else if (mPlaybackRate < 0.0 &&
              (currentTime.IsNull())) {
     mHoldTime.SetValue(TimeDuration(SourceContentEnd()));
   } else if (mPlaybackRate == 0.0 && currentTime.IsNull()) {
     mHoldTime.SetValue(TimeDuration(0));
   }
 
   if (mHoldTime.IsNull()) {
     return;
   }
 
-  // Clear ready promise. We'll create a new one lazily.
-  mReady = nullptr;
-
   // Clear the start time until we resolve a new one
   mStartTime.SetNull();
 
+  if (!reuseReadyPromise) {
+    // Clear ready promise. We'll create a new one lazily.
+    mReady = nullptr;
+  }
+
   mPendingState = PendingState::PlayPending;
 
   nsIDocument* doc = GetRenderedDocument();
   if (!doc) {
     TriggerOnNextTick(Nullable<TimeDuration>());
     return;
   }