diff --git a/dlls/dwmapi/dwmapi.spec b/dlls/dwmapi/dwmapi.spec
index 7c613d0..a5082d4 100644
--- a/dlls/dwmapi/dwmapi.spec
+++ b/dlls/dwmapi/dwmapi.spec
@@ -21,7 +21,7 @@
 120 stub @
 
 @ stub DwmAttachMilContent
-@ stub DwmDefWindowProc
+@ stdcall DwmDefWindowProc(ptr long ptr ptr ptr)
 @ stub DwmDetachMilContent
 @ stub DwmEnableBlurBehindWindow
 @ stdcall DwmEnableMMCSS(long)
diff --git a/dlls/dwmapi/dwmapi_main.c b/dlls/dwmapi/dwmapi_main.c
index 6042028..57c7c31 100644
--- a/dlls/dwmapi/dwmapi_main.c
+++ b/dlls/dwmapi/dwmapi_main.c
@@ -159,3 +159,13 @@ HRESULT WINAPI DwmGetGraphicsStreamTransformHint(UINT uIndex, MilMatrix3x2D *pTr
 
     return E_NOTIMPL;
 }
+
+/**********************************************************************
+ *           DwmDefWindowProc         (DWMAPI.@)
+ */
+BOOL WINAPI DwmDefWindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam, LRESULT *plResult)
+{
+    FIXME("(%p, %d, %lx, %lx, %p) stub\n", hwnd, msg, wParam, lParam, plResult);
+
+    return FALSE;
+}