diff --git a/reactos/dll/win32/dwmapi/dwmapi.spec b/reactos/dll/win32/dwmapi/dwmapi.spec
index 63ee2f54d33..f1c800f72cc 100644
--- a/reactos/dll/win32/dwmapi/dwmapi.spec
+++ b/reactos/dll/win32/dwmapi/dwmapi.spec
@@ -24,7 +24,7 @@
 @ stub DwmDefWindowProc
 @ stub DwmDetachMilContent
 @ stub DwmEnableBlurBehindWindow
-@ stub DwmEnableMMCSS
+@ stdcall DwmEnableMMCSS(long)
 @ stdcall DwmExtendFrameIntoClientArea(long ptr)
 @ stdcall DwmFlush()
 @ stdcall DwmGetColorizationColor(ptr long)
diff --git a/reactos/dll/win32/dwmapi/dwmapi_main.c b/reactos/dll/win32/dwmapi/dwmapi_main.c
index e306c56709f..d7d6f5b6e2b 100644
--- a/reactos/dll/win32/dwmapi/dwmapi_main.c
+++ b/reactos/dll/win32/dwmapi/dwmapi_main.c
@@ -93,7 +93,7 @@ HRESULT WINAPI DwmGetColorizationColor(DWORD *colorization, BOOL opaque_blend)
 /**********************************************************************
  *                  DwmFlush              (DWMAPI.@)
  */
-HRESULT WINAPI DwmFlush()
+HRESULT WINAPI DwmFlush(void)
 {
     FIXME("() stub\n");
 
@@ -119,3 +119,13 @@ HRESULT WINAPI DwmUnregisterThumbnail(HTHUMBNAIL thumbnail)
 
     return E_NOTIMPL;
 }
+
+/**********************************************************************
+ *           DwmEnableMMCSS         (DWMAPI.@)
+ */
+HRESULT WINAPI DwmEnableMMCSS(BOOL enableMMCSS)
+{
+    FIXME("(%d) stub\n", enableMMCSS);
+
+    return S_OK;
+}