diff --git a/widget/android/AndroidVsync.cpp b/widget/android/AndroidVsync.cpp
index d0d88f8ccaaa..6aed5f1e539c 100644
--- a/widget/android/AndroidVsync.cpp
+++ b/widget/android/AndroidVsync.cpp
@@ -6,6 +6,7 @@
 
 #include "AndroidVsync.h"
 
+#include "AndroidBridge.h"
 #include "nsTArray.h"
 
 /**
@@ -113,6 +114,8 @@ void AndroidVsync::Impl::UpdateObservingVsync() {
 
 // Always called on the Java UI thread.
 void AndroidVsync::NotifyVsync(int64_t aFrameTimeNanos) {
+  MOZ_ASSERT(AndroidBridge::IsJavaUiThread());
+
   // Convert aFrameTimeNanos to a TimeStamp. The value converts trivially to
   // the internal ticks representation of TimeStamp_posix; both use the
   // monotonic clock and are in nanoseconds.
@@ -131,13 +134,13 @@ void AndroidVsync::NotifyVsync(int64_t aFrameTimeNanos) {
 }
 
 void AndroidVsync::OnMaybeUpdateRefreshRate() {
-  // Do not keep the lock held while calling OnVsync.
+  MOZ_ASSERT(NS_IsMainThread());
+
+  auto impl = mImpl.Lock();
+
   nsTArray<Observer*> observers;
-  {
-    auto impl = mImpl.Lock();
-    observers.AppendElements(impl->mInputObservers);
-    observers.AppendElements(impl->mRenderObservers);
-  }
+  observers.AppendElements(impl->mRenderObservers);
+
   for (Observer* observer : observers) {
     observer->OnMaybeUpdateRefreshRate();
   }