diff --git a/dlls/api-ms-win-core-winrt-l1-1-0/api-ms-win-core-winrt-l1-1-0.spec b/dlls/api-ms-win-core-winrt-l1-1-0/api-ms-win-core-winrt-l1-1-0.spec
index 978c3dc6d07..88139fbddf1 100644
--- a/dlls/api-ms-win-core-winrt-l1-1-0/api-ms-win-core-winrt-l1-1-0.spec
+++ b/dlls/api-ms-win-core-winrt-l1-1-0/api-ms-win-core-winrt-l1-1-0.spec
@@ -1,6 +1,6 @@
 @ stdcall RoActivateInstance(ptr ptr) combase.RoActivateInstance
 @ stdcall RoGetActivationFactory(ptr ptr ptr) combase.RoGetActivationFactory
-@ stub RoGetApartmentIdentifier
+@ stdcall RoGetApartmentIdentifier(ptr) combase.RoGetApartmentIdentifier
 @ stdcall RoInitialize(long) combase.RoInitialize
 @ stub RoRegisterActivationFactories
 @ stub RoRegisterForApartmentShutdown
diff --git a/dlls/combase/combase.spec b/dlls/combase/combase.spec
index f42bdae605b..ff892322f78 100644
--- a/dlls/combase/combase.spec
+++ b/dlls/combase/combase.spec
@@ -250,7 +250,7 @@
 @ stub RoGetActivatableClassRegistration
 @ stdcall RoGetActivationFactory(ptr ptr ptr)
 @ stub RoGetAgileReference
-@ stub RoGetApartmentIdentifier
+@ stdcall RoGetApartmentIdentifier(ptr)
 @ stub RoGetErrorReportingFlags
 @ stub RoGetMatchingRestrictedErrorInfo
 @ stdcall RoGetParameterizedTypeInstanceIID(long ptr ptr ptr ptr)
diff --git a/dlls/combase/roapi.c b/dlls/combase/roapi.c
index bfd07fb3f4e..9cceb8206a8 100644
--- a/dlls/combase/roapi.c
+++ b/dlls/combase/roapi.c
@@ -218,3 +218,17 @@ HRESULT WINAPI RoActivateInstance(HSTRING classid, IInspectable **instance)
 
     return hr;
 }
+
+/***********************************************************************
+ *      RoGetApartmentIdentifier (combase.@)
+ */
+HRESULT WINAPI RoGetApartmentIdentifier(UINT64 *identifier)
+{
+    FIXME("(%p): stub\n", identifier);
+
+    if (!identifier)
+        return E_INVALIDARG;
+
+    *identifier = 0xdeadbeef;
+    return S_OK;
+}