diff --git a/gfx/layers/apz/public/APZSampler.h b/gfx/layers/apz/public/APZSampler.h
index 46c2f9b2ff00..c2d25a4e6901 100644
--- a/gfx/layers/apz/public/APZSampler.h
+++ b/gfx/layers/apz/public/APZSampler.h
@@ -52,8 +52,8 @@ public:
    */
   static void SetSamplerThread(const wr::WrWindowId& aWindowId);
 
-  bool PushStateToWR(wr::TransactionWrapper& aTxn,
-                     const TimeStamp& aSampleTime);
+  void SetSampleTime(const TimeStamp& aSampleTime);
+  bool PushStateToWR(wr::TransactionWrapper& aTxn);
 
   bool SampleAnimations(const LayerMetricsWrapper& aLayer,
                         const TimeStamp& aSampleTime);
@@ -125,6 +125,9 @@ private:
   mutable bool mSamplerThreadQueried;
 #endif
 
+  Mutex mSampleTimeLock;
+  // Can only be accessed or modified while holding mSampleTimeLock.
+  TimeStamp mSampleTime;
 };
 
 } // namespace layers
diff --git a/gfx/layers/apz/src/APZSampler.cpp b/gfx/layers/apz/src/APZSampler.cpp
index 39c6cd406cd3..59416a3badda 100644
--- a/gfx/layers/apz/src/APZSampler.cpp
+++ b/gfx/layers/apz/src/APZSampler.cpp
@@ -27,6 +27,7 @@ APZSampler::APZSampler(const RefPtr<APZCTreeManager>& aApz)
 #ifdef DEBUG
   , mSamplerThreadQueried(false)
 #endif
+  , mSampleTimeLock("APZSampler::mSampleTimeLock")
 {
   MOZ_ASSERT(aApz);
   mApz->SetSampler(this);
@@ -61,13 +62,31 @@ APZSampler::SetSamplerThread(const wr::WrWindowId& aWindowId)
   }
 }
 
+void
+APZSampler::SetSampleTime(const TimeStamp& aSampleTime)
+{
+  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
+  MutexAutoLock lock(mSampleTimeLock);
+  mSampleTime = aSampleTime;
+}
+
 bool
-APZSampler::PushStateToWR(wr::TransactionWrapper& aTxn,
-                          const TimeStamp& aSampleTime)
+APZSampler::PushStateToWR(wr::TransactionWrapper& aTxn)
 {
   // This function will be removed eventually since we'll have WR pull
   // the transforms from APZ instead.
-  return mApz->PushStateToWR(aTxn, aSampleTime);
+  AssertOnSamplerThread();
+  TimeStamp sampleTime;
+  { // scope lock
+    MutexAutoLock lock(mSampleTimeLock);
+
+    // If mSampleTime is null we're in a startup phase where the
+    // WebRenderBridgeParent hasn't yet provided us with a sample time.
+    // If we're that early there probably aren't any APZ animations happening
+    // anyway, so using Timestamp::Now() should be fine.
+    sampleTime = mSampleTime.IsNull() ? TimeStamp::Now() : mSampleTime;
+  }
+  return mApz->PushStateToWR(aTxn, sampleTime);
 }
 
 bool
diff --git a/gfx/layers/wr/WebRenderBridgeParent.cpp b/gfx/layers/wr/WebRenderBridgeParent.cpp
index 230b0798bbfd..ce7dfe17ec8b 100644
--- a/gfx/layers/wr/WebRenderBridgeParent.cpp
+++ b/gfx/layers/wr/WebRenderBridgeParent.cpp
@@ -548,11 +548,12 @@ WebRenderBridgeParent::PushAPZStateToWR(wr::TransactionBuilder& aTxn)
     if (frameInterval != TimeDuration::Forever()) {
       animationTime += frameInterval;
     }
+    apz->SetSampleTime(animationTime);
     // The TransactionWrapper shares the underlying transaction object with
     // aTxn. When we exit this scope the TransactionWrapper is destroyed but
     // the underlying transaction lives on in aTxn.
     wr::TransactionWrapper txn(aTxn.Raw());
-    return apz->PushStateToWR(txn, animationTime);
+    return apz->PushStateToWR(txn);
   }
   return false;
 }