diff --git a/gfx/layers/CompositorTypes.h b/gfx/layers/CompositorTypes.h
index d4e6aa5ce630..0765c751c943 100644
--- a/gfx/layers/CompositorTypes.h
+++ b/gfx/layers/CompositorTypes.h
@@ -252,7 +252,12 @@ enum class OpenMode : uint8_t {
   OPEN_WRITE       = 0x2,
   OPEN_READ_WRITE  = OPEN_READ|OPEN_WRITE,
   OPEN_READ_ONLY   = OPEN_READ,
-  OPEN_WRITE_ONLY  = OPEN_WRITE
+  OPEN_WRITE_ONLY  = OPEN_WRITE,
+
+  // This is only used in conjunction with OMTP to indicate that the DrawTarget
+  // that is being borrowed will be painted asynchronously, and so will outlive
+  // the write lock.
+  OPEN_ASYNC_WRITE = 0x04
 };
 MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(OpenMode)
 
diff --git a/gfx/layers/client/ClientPaintedLayer.cpp b/gfx/layers/client/ClientPaintedLayer.cpp
index b4a1f5648819..24476f273f3c 100644
--- a/gfx/layers/client/ClientPaintedLayer.cpp
+++ b/gfx/layers/client/ClientPaintedLayer.cpp
@@ -185,7 +185,7 @@ ClientPaintedLayer::PaintThebes(nsTArray<ReadbackProcessor::Update>* aReadbackUp
 bool
 ClientPaintedLayer::PaintOffMainThread()
 {
-  mContentClient->BeginPaint();
+  mContentClient->BeginAsyncPaint();
 
   uint32_t flags = GetPaintFlags();
 
diff --git a/gfx/layers/client/ContentClient.cpp b/gfx/layers/client/ContentClient.cpp
index 26323d5edd1f..2f1b7b138c10 100644
--- a/gfx/layers/client/ContentClient.cpp
+++ b/gfx/layers/client/ContentClient.cpp
@@ -91,9 +91,16 @@ ContentClient::CreateContentClient(CompositableForwarder* aForwarder)
   return MakeAndAddRef<ContentClientSingleBuffered>(aForwarder);
 }
 
+void
+ContentClient::BeginAsyncPaint()
+{
+  mInAsyncPaint = true;
+}
+
 void
 ContentClient::EndPaint(nsTArray<ReadbackProcessor::Update>* aReadbackUpdates)
 {
+  mInAsyncPaint = false;
 }
 
 void
@@ -238,6 +245,13 @@ ContentClientRemoteBuffer::BeginPaint()
   }
 }
 
+void
+ContentClientRemoteBuffer::BeginAsyncPaint()
+{
+  BeginPaint();
+  mInAsyncPaint = true;
+}
+
 void
 ContentClientRemoteBuffer::EndPaint(nsTArray<ReadbackProcessor::Update>* aReadbackUpdates)
 {
@@ -349,14 +363,19 @@ ContentClientRemoteBuffer::CreateBuffer(ContentType aType,
     return;
   }
 
+  OpenMode mode = OpenMode::OPEN_READ_WRITE;
+  if (mInAsyncPaint) {
+    mode |= OpenMode::OPEN_ASYNC_WRITE;
+  }
+
   // We just created the textures and we are about to get their draw targets
   // so we have to lock them here.
-  DebugOnly<bool> locked = mTextureClient->Lock(OpenMode::OPEN_READ_WRITE);
+  DebugOnly<bool> locked = mTextureClient->Lock(mode);
   MOZ_ASSERT(locked, "Could not lock the TextureClient");
 
   *aBlackDT = mTextureClient->BorrowDrawTarget();
   if (aFlags & BUFFER_COMPONENT_ALPHA) {
-    locked = mTextureClientOnWhite->Lock(OpenMode::OPEN_READ_WRITE);
+    locked = mTextureClientOnWhite->Lock(mode);
     MOZ_ASSERT(locked, "Could not lock the second TextureClient for component alpha");
 
     *aWhiteDT = mTextureClientOnWhite->BorrowDrawTarget();
@@ -430,14 +449,18 @@ ContentClientRemoteBuffer::SwapBuffers(const nsIntRegion& aFrontUpdatedRegion)
 bool
 ContentClientRemoteBuffer::LockBuffers()
 {
+  OpenMode mode = OpenMode::OPEN_READ_WRITE;
+  if (mInAsyncPaint) {
+    mode |= OpenMode::OPEN_ASYNC_WRITE;
+  }
   if (mTextureClient) {
-    bool locked = mTextureClient->Lock(OpenMode::OPEN_READ_WRITE);
+    bool locked = mTextureClient->Lock(mode);
     if (!locked) {
       return false;
     }
   }
   if (mTextureClientOnWhite) {
-    bool locked = mTextureClientOnWhite->Lock(OpenMode::OPEN_READ_WRITE);
+    bool locked = mTextureClientOnWhite->Lock(mode);
     if (!locked) {
       UnlockBuffers();
       return false;
@@ -553,6 +576,13 @@ ContentClientDoubleBuffered::BeginPaint()
   mBufferRotation = mFrontBufferRotation;
 }
 
+void
+ContentClientDoubleBuffered::BeginAsyncPaint()
+{
+  BeginPaint();
+  mInAsyncPaint = true;
+}
+
 // Sync front/back buffers content
 // After executing, the new back buffer has the same (interesting) pixels as
 // the new front buffer, and mValidRegion et al. are correct wrt the new
diff --git a/gfx/layers/client/ContentClient.h b/gfx/layers/client/ContentClient.h
index 96ed41b4448f..9354467c0bd8 100644
--- a/gfx/layers/client/ContentClient.h
+++ b/gfx/layers/client/ContentClient.h
@@ -82,7 +82,8 @@ public:
   static already_AddRefed<ContentClient> CreateContentClient(CompositableForwarder* aFwd);
 
   explicit ContentClient(CompositableForwarder* aForwarder)
-  : CompositableClient(aForwarder)
+  : CompositableClient(aForwarder),
+    mInAsyncPaint(false)
   {}
   virtual ~ContentClient()
   {}
@@ -103,7 +104,11 @@ public:
 
   // call before and after painting into this content client
   virtual void BeginPaint() {}
+  virtual void BeginAsyncPaint();
   virtual void EndPaint(nsTArray<ReadbackProcessor::Update>* aReadbackUpdates = nullptr);
+
+protected:
+  bool mInAsyncPaint;
 };
 
 /**
@@ -243,6 +248,7 @@ public:
    * are affected by mapping/unmapping.
    */
   virtual void BeginPaint() override;
+  virtual void BeginAsyncPaint() override;
   virtual void EndPaint(nsTArray<ReadbackProcessor::Update>* aReadbackUpdates = nullptr) override;
 
   virtual void Updated(const nsIntRegion& aRegionToDraw,
@@ -347,6 +353,7 @@ public:
   virtual void SwapBuffers(const nsIntRegion& aFrontUpdatedRegion) override;
 
   virtual void BeginPaint() override;
+  virtual void BeginAsyncPaint() override;
 
   virtual void FinalizeFrame(const nsIntRegion& aRegionToDraw) override;
 
diff --git a/gfx/layers/client/TextureClient.cpp b/gfx/layers/client/TextureClient.cpp
index 615021446e26..fdfd43891c04 100644
--- a/gfx/layers/client/TextureClient.cpp
+++ b/gfx/layers/client/TextureClient.cpp
@@ -509,7 +509,7 @@ TextureClient::Lock(OpenMode aMode)
 
   auto format = GetFormat();
   if (mIsLocked && CanExposeDrawTarget() &&
-      aMode == OpenMode::OPEN_READ_WRITE &&
+      (aMode & OpenMode::OPEN_READ_WRITE) == OpenMode::OPEN_READ_WRITE &&
       NS_IsMainThread() &&
       // the formats that we apparently expect, in the cairo backend. Any other
       // format will trigger an assertion in GfxFormatToCairoFormat.
@@ -557,7 +557,8 @@ TextureClient::Unlock()
     mBorrowedDrawTarget->DetachAllSnapshots();
     // If this assertion is hit, it means something is holding a strong reference
     // to our DrawTarget externally, which is not allowed.
-    MOZ_ASSERT(mBorrowedDrawTarget->refCount() <= mExpectedDtRefs);
+    MOZ_ASSERT_IF(!(mOpenMode & OpenMode::OPEN_ASYNC_WRITE),
+                  mBorrowedDrawTarget->refCount() <= mExpectedDtRefs);
 
     mBorrowedDrawTarget = nullptr;
   }