--- a/dom/media/eme/CDMProxy.cpp
+++ b/dom/media/eme/CDMProxy.cpp
@@ -439,17 +439,23 @@ CDMProxy::OnExpirationChange(const nsASt
   MOZ_ASSERT(NS_IsMainThread());
   NS_WARNING("CDMProxy::OnExpirationChange() not implemented");
 }
 
 void
 CDMProxy::OnSessionClosed(const nsAString& aSessionId)
 {
   MOZ_ASSERT(NS_IsMainThread());
-  NS_WARNING("CDMProxy::OnSessionClosed() not implemented");
+  if (mKeys.IsNull()) {
+    return;
+  }
+  nsRefPtr<dom::MediaKeySession> session(mKeys->GetSession(aSessionId));
+  if (session) {
+    session->OnClosed();
+  }
 }
 
 static void
 LogToConsole(const nsAString& aMsg)
 {
   nsCOMPtr<nsIConsoleService> console(
     do_GetService("@mozilla.org/consoleservice;1"));
   if (!console) {