diff --git a/reactos/include/psdk/winnt.h b/reactos/include/psdk/winnt.h
index bd0fac136b9..f856b079970 100644
--- a/reactos/include/psdk/winnt.h
+++ b/reactos/include/psdk/winnt.h
@@ -3411,6 +3411,12 @@ typedef LONG
     struct _EXCEPTION_POINTERS *ExceptionInfo
 );
 
+typedef struct _GROUP_AFFINITY {
+  KAFFINITY Mask;
+  WORD Group;
+  WORD Reserved[3];
+} GROUP_AFFINITY, *PGROUP_AFFINITY;
+
 typedef struct _EVENTLOGRECORD {
 	DWORD Length;
 	DWORD Reserved;