diff --git a/content/media/MediaDecoder.cpp b/content/media/MediaDecoder.cpp
index 5792fa129896..d25be066e6bc 100644
--- a/content/media/MediaDecoder.cpp
+++ b/content/media/MediaDecoder.cpp
@@ -283,6 +283,7 @@ double MediaDecoder::GetDuration()
 
 int64_t MediaDecoder::GetMediaDuration()
 {
+  NS_ENSURE_TRUE(GetStateMachine(), -1);
   return GetStateMachine()->GetDuration();
 }
 
@@ -429,6 +430,7 @@ nsresult MediaDecoder::Load(MediaResource* aResource,
 nsresult MediaDecoder::InitializeStateMachine(MediaDecoder* aCloneDonor)
 {
   MOZ_ASSERT(NS_IsMainThread());
+  NS_ASSERTION(mDecoderStateMachine, "Cannot initialize null state machine!");
 
   MediaDecoder* cloneDonor = static_cast<MediaDecoder*>(aCloneDonor);
   if (NS_FAILED(mDecoderStateMachine->Init(cloneDonor ?
@@ -968,6 +970,7 @@ void MediaDecoder::NotifyPrincipalChanged()
 
 void MediaDecoder::NotifyBytesConsumed(int64_t aBytes)
 {
+  NS_ENSURE_TRUE(mDecoderStateMachine, );
   ReentrantMonitorAutoEnter mon(GetReentrantMonitor());
   MOZ_ASSERT(OnStateMachineThread() || mDecoderStateMachine->OnDecodeThread());
   if (!mIgnoreProgressData) {
@@ -1199,6 +1202,7 @@ void MediaDecoder::SetDuration(double aDuration)
 
 void MediaDecoder::SetMediaDuration(int64_t aDuration)
 {
+  NS_ENSURE_TRUE(GetStateMachine(), );
   GetStateMachine()->SetDuration(aDuration);
 }
 
@@ -1229,6 +1233,7 @@ bool MediaDecoder::IsTransportSeekable()
 
 bool MediaDecoder::IsMediaSeekable()
 {
+  NS_ENSURE_TRUE(GetStateMachine(), false);
   ReentrantMonitorAutoEnter mon(GetReentrantMonitor());
   MOZ_ASSERT(OnDecodeThread() || NS_IsMainThread());
   return mMediaSeekable;
@@ -1265,6 +1270,7 @@ void MediaDecoder::SetFragmentEndTime(double aTime)
 
 void MediaDecoder::SetMediaEndTime(int64_t aTime)
 {
+  NS_ENSURE_TRUE(GetStateMachine(), );
   GetStateMachine()->SetMediaEndTime(aTime);
 }
 
@@ -1367,6 +1373,7 @@ void MediaDecoder::SetPreservesPitch(bool aPreservesPitch)
 }
 
 bool MediaDecoder::OnDecodeThread() const {
+  NS_ENSURE_TRUE(mDecoderStateMachine, false);
   return mDecoderStateMachine->OnDecodeThread();
 }
 
@@ -1426,10 +1433,12 @@ MediaDecoderStateMachine* MediaDecoder::GetStateMachine() const {
 }
 
 bool MediaDecoder::IsShutdown() const {
+  NS_ENSURE_TRUE(GetStateMachine(), true);
   return GetStateMachine()->IsShutdown();
 }
 
 int64_t MediaDecoder::GetEndMediaTime() const {
+  NS_ENSURE_TRUE(GetStateMachine(), -1);
   return GetStateMachine()->GetEndMediaTime();
 }
 
diff --git a/content/media/dash/DASHRepDecoder.cpp b/content/media/dash/DASHRepDecoder.cpp
index b913446d7f47..d18a96c55488 100644
--- a/content/media/dash/DASHRepDecoder.cpp
+++ b/content/media/dash/DASHRepDecoder.cpp
@@ -473,7 +473,14 @@ ReentrantMonitor&
 DASHRepDecoder::GetReentrantMonitor()
 {
   NS_ASSERTION(mMainDecoder, "Can't get monitor if main decoder is null!");
-  return mMainDecoder->GetReentrantMonitor();
+  if (mMainDecoder) {
+    return mMainDecoder->GetReentrantMonitor();
+  } else {
+    // XXX If mMainDecoder is gone, most likely we're past shutdown and
+    // a waiting function has been wakened. Just return this decoder's own
+    // monitor and let the function complete.
+    return MediaDecoder::GetReentrantMonitor();
+  }
 }
 
 mozilla::layers::ImageContainer*