--- a/dom/media/gmp/GMPContentChild.cpp
+++ b/dom/media/gmp/GMPContentChild.cpp
@@ -94,17 +94,17 @@ GMPContentChild::DeallocPGMPVideoEncoder
 }
 
 mozilla::ipc::IPCResult
 GMPContentChild::RecvPGMPDecryptorConstructor(PGMPDecryptorChild* aActor)
 {
   GMPDecryptorChild* child = static_cast<GMPDecryptorChild*>(aActor);
 
   void* ptr = nullptr;
-  GMPErr err = mGMPChild->GetAPI(GMP_API_DECRYPTOR, nullptr, &ptr, aActor->Id());
+  GMPErr err = mGMPChild->GetAPI(GMP_API_DECRYPTOR, nullptr, &ptr, child->DecryptorId());
   if (err != GMPNoErr || !ptr) {
     NS_WARNING("GMPGetAPI call failed trying to construct decryptor.");
     return IPC_FAIL_NO_REASON(this);
   }
   child->Init(static_cast<GMPDecryptor*>(ptr));
 
   return IPC_OK();
 }

--- a/dom/media/gmp/GMPDecryptorChild.cpp
+++ b/dom/media/gmp/GMPDecryptorChild.cpp
@@ -15,19 +15,22 @@
 #define ON_GMP_THREAD() (mPlugin->GMPMessageLoop() == MessageLoop::current())
 
 #define CALL_ON_GMP_THREAD(_func, ...) \
   CallOnGMPThread(&GMPDecryptorChild::_func, __VA_ARGS__)
 
 namespace mozilla {
 namespace gmp {
 
+static uint32_t sDecryptorCount = 1;
+
 GMPDecryptorChild::GMPDecryptorChild(GMPContentChild* aPlugin)
   : mSession(nullptr)
   , mPlugin(aPlugin)
+  , mDecryptorId(sDecryptorCount++)
 {
   MOZ_ASSERT(mPlugin);
 }
 
 GMPDecryptorChild::~GMPDecryptorChild()
 {
 }
 
@@ -68,17 +71,17 @@ void
 GMPDecryptorChild::Init(GMPDecryptor* aSession)
 {
   MOZ_ASSERT(aSession);
   mSession = aSession;
   // The ID of this decryptor is the IPDL actor ID. Note it's unique inside
   // the child process, but not necessarily across all gecko processes. However,
   // since GMPDecryptors are segregated by node ID/origin, we shouldn't end up
   // with clashes in the content process.
-  SendSetDecryptorId(Id());
+  SendSetDecryptorId(DecryptorId());
 }
 
 void
 GMPDecryptorChild::SetSessionId(uint32_t aCreateSessionToken,
                                 const char* aSessionId,
                                 uint32_t aSessionIdLength)
 {
   CALL_ON_GMP_THREAD(SendSetSessionId,

--- a/dom/media/gmp/GMPDecryptorChild.h
+++ b/dom/media/gmp/GMPDecryptorChild.h
@@ -70,16 +70,17 @@ public:
 
   void Decrypted(GMPBuffer* aBuffer, GMPErr aResult) override;
 
   void BatchedKeyStatusChanged(const char* aSessionId,
                                uint32_t aSessionIdLength,
                                const GMPMediaKeyInfo* aKeyInfos,
                                uint32_t aKeyInfosLength) override;
 
+  uint32_t DecryptorId() const { return mDecryptorId; }
 private:
   ~GMPDecryptorChild();
 
   // GMPDecryptorChild
   mozilla::ipc::IPCResult RecvInit(const bool& aDistinctiveIdentifierRequired,
                                    const bool& aPersistentStateRequired) override;
 
   mozilla::ipc::IPCResult RecvCreateSession(const uint32_t& aCreateSessionToken,
@@ -117,14 +118,16 @@ private:
 
   template<typename MethodType, typename... ParamType>
   void CallOnGMPThread(MethodType, ParamType&&...);
 
   // GMP's GMPDecryptor implementation.
   // Only call into this on the (GMP process) main thread.
   GMPDecryptor* mSession;
   GMPContentChild* mPlugin;
+
+  const uint32_t mDecryptorId;
 };
 
 } // namespace gmp
 } // namespace mozilla
 
 #endif // GMPDecryptorChild_h_