diff --git a/reactos/include/ddk/ddrawint.h b/reactos/include/ddk/ddrawint.h
index c2a5ff4f064..682fd6b955a 100644
--- a/reactos/include/ddk/ddrawint.h
+++ b/reactos/include/ddk/ddrawint.h
@@ -57,7 +57,10 @@ extern "C" {
 #define MAKE_HRESULT(sev,fac,code) ((HRESULT) (((unsigned long)(sev)<<31) | ((unsigned long)(fac)<<16) | ((unsigned long)(code))) )
 #endif
 
+#ifndef FLATPTR_DEFINED
 typedef ULONG_PTR FLATPTR;
+#define FLATPTR_DEFINED
+#endif
 
 typedef struct _DD_VIDEOPORT_LOCAL   *PDD_VIDEOPORT_LOCAL;
 
diff --git a/reactos/include/ddk/dmemmgr.h b/reactos/include/ddk/dmemmgr.h
index ed339cfa597..7c5679b256a 100644
--- a/reactos/include/ddk/dmemmgr.h
+++ b/reactos/include/ddk/dmemmgr.h
@@ -17,10 +17,21 @@ extern "C" {
 #endif
 
 #ifndef __NTDDKCOMP__
+
+#ifndef FLATPTR_DEFINED
 typedef ULONG_PTR FLATPTR;
+#define FLATPTR_DEFINED
+#endif
+
 typedef struct _VIDMEM *LPVIDMEM;
+
 #else
+
+#ifndef FLATPTR_DEFINED
 typedef ULONG_PTR FLATPTR;
+#define FLATPTR_DEFINED
+#endif
+
 typedef struct _VIDEOMEMORY *LPVIDMEM;
 #endif
 
@@ -115,15 +126,6 @@ typedef struct _VMEMHEAP
     DWORD dwAgpCommitMaskSize;
 } VMEMHEAP, *LPVMEMHEAP;
 
-typedef struct _DD_GETHEAPALIGNMENTDATA
-{
-    ULONG_PTR dwInstance;
-    DWORD dwHeap;
-    HRESULT ddRVal;
-    VOID* GetHeapAlignment;
-    HEAPALIGNMENT Alignment;
-} DD_GETHEAPALIGNMENTDATA, *PDD_GETHEAPALIGNMENTDATA;
-
 extern void WINAPI VidMemFree( LPVMEMHEAP pvmh, FLATPTR ptr);
 extern FLATPTR WINAPI VidMemAlloc( LPVMEMHEAP pvmh, DWORD width, DWORD height);