diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java
index 441202d3268f..af50d9a6631e 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/media/Codec.java
@@ -324,7 +324,10 @@ import org.mozilla.gecko.gfx.GeckoSurface;
             sample.dispose();
         }
 
-        private void onFormatChanged(final MediaFormat format) {
+        private synchronized void onFormatChanged(final MediaFormat format) {
+            if (mStopped) {
+                return;
+            }
             try {
                 mCallbacks.onOutputFormatChanged(new FormatParam(format));
             } catch (RemoteException re) {