diff --git a/dom/quota/DirectoryLock.h b/dom/quota/DirectoryLock.h
index e53a9748d501..b7fbd03d4a26 100644
--- a/dom/quota/DirectoryLock.h
+++ b/dom/quota/DirectoryLock.h
@@ -46,7 +46,7 @@ class NS_NO_VTABLE DirectoryLock {
 
   virtual void AssertIsAcquiredExclusively() = 0;
 
-  virtual void Drop() = 0;
+  virtual RefPtr<BoolPromise> Drop() = 0;
 
   virtual void OnInvalidate(std::function<void()>&& aCallback) = 0;
 
diff --git a/dom/quota/DirectoryLockImpl.cpp b/dom/quota/DirectoryLockImpl.cpp
index ddfe430aac27..27c9b76d94a9 100644
--- a/dom/quota/DirectoryLockImpl.cpp
+++ b/dom/quota/DirectoryLockImpl.cpp
@@ -295,15 +295,20 @@ void DirectoryLockImpl::AssertIsAcquiredExclusively() {
 }
 #endif
 
-void DirectoryLockImpl::Drop() {
+RefPtr<BoolPromise> DirectoryLockImpl::Drop() {
   AssertIsOnOwningThread();
   MOZ_ASSERT_IF(!mRegistered, mBlocking.IsEmpty());
 
   mDropped.Flip();
 
-  if (mRegistered) {
-    Unregister();
-  }
+  return InvokeAsync(GetCurrentSerialEventTarget(), __func__,
+                     [self = RefPtr(this)]() {
+                       if (self->mRegistered) {
+                         self->Unregister();
+                       }
+
+                       return BoolPromise::CreateAndResolve(true, __func__);
+                     });
 }
 
 void DirectoryLockImpl::OnInvalidate(std::function<void()>&& aCallback) {
diff --git a/dom/quota/DirectoryLockImpl.h b/dom/quota/DirectoryLockImpl.h
index dbf059665e4d..1fdb804f6a4c 100644
--- a/dom/quota/DirectoryLockImpl.h
+++ b/dom/quota/DirectoryLockImpl.h
@@ -202,7 +202,7 @@ class DirectoryLockImpl final : public ClientDirectoryLock,
   }
 #endif
 
-  void Drop() override;
+  RefPtr<BoolPromise> Drop() override;
 
   void OnInvalidate(std::function<void()>&& aCallback) override;
 
diff --git a/dom/quota/test/gtest/TestDirectoryLock.cpp b/dom/quota/test/gtest/TestDirectoryLock.cpp
index fe6d1aa8f4e5..fa03496f9bd3 100644
--- a/dom/quota/test/gtest/TestDirectoryLock.cpp
+++ b/dom/quota/test/gtest/TestDirectoryLock.cpp
@@ -19,7 +19,7 @@ class DOM_Quota_DirectoryLock : public QuotaManagerDependencyFixture {
   static void TearDownTestCase() { ASSERT_NO_FATAL_FAILURE(ShutdownFixture()); }
 };
 
-// Test that Drop unregisters directory lock synchronously.
+// Test that Drop unregisters directory lock asynchronously.
 TEST_F(DOM_Quota_DirectoryLock, Drop_Timing) {
   PerformOnBackgroundThread([]() {
     QuotaManager* quotaManager = QuotaManager::Get();
@@ -41,7 +41,7 @@ TEST_F(DOM_Quota_DirectoryLock, Drop_Timing) {
 
     SpinEventLoopUntil("Promise is fulfilled"_ns, [&done]() { return done; });
 
-    exclusiveDirectoryLock->Drop();
+    auto exclusiveDirectoryLockDropPromise = exclusiveDirectoryLock->Drop();
     exclusiveDirectoryLock = nullptr;
 
     RefPtr<UniversalDirectoryLock> sharedDirectoryLock =
@@ -50,6 +50,18 @@ TEST_F(DOM_Quota_DirectoryLock, Drop_Timing) {
             OriginScope::FromNull(), Nullable<Client::Type>(),
             /* aExclusive */ false, DirectoryLockCategory::None);
 
+    ASSERT_TRUE(sharedDirectoryLock->MustWait());
+
+    done = false;
+
+    exclusiveDirectoryLockDropPromise->Then(
+        GetCurrentSerialEventTarget(), __func__,
+        [&done](const BoolPromise::ResolveOrRejectValue& aValue) {
+          done = true;
+        });
+
+    SpinEventLoopUntil("Promise is fulfilled"_ns, [&done]() { return done; });
+
     ASSERT_FALSE(sharedDirectoryLock->MustWait());
 
     sharedDirectoryLock = nullptr;