diff --git a/dlls/ddraw/ddraw/main.c b/dlls/ddraw/ddraw/main.c
index d3492a994c8..b2d76f1260e 100644
--- a/dlls/ddraw/ddraw/main.c
+++ b/dlls/ddraw/ddraw/main.c
@@ -283,7 +283,8 @@ create_texture(IDirectDrawImpl* This, const DDSURFACEDESC2 *pDDSD,
     if ((pDDSD->dwFlags&(DDSD_HEIGHT|DDSD_WIDTH)) != (DDSD_HEIGHT|DDSD_WIDTH))
 	return DDERR_INVALIDPARAMS;
 
-    ddsd = *pDDSD;
+    ddsd.dwSize = sizeof(ddsd);
+    DD_STRUCT_COPY_BYSIZE((&ddsd),pDDSD);
 
     if (!(ddsd.dwFlags & DDSD_PIXELFORMAT))
     {
@@ -365,7 +366,8 @@ create_primary(IDirectDrawImpl* This, LPDDSURFACEDESC2 pDDSD,
     if (pDDSD->dwFlags & (DDSD_HEIGHT|DDSD_WIDTH|DDSD_PIXELFORMAT))
 	return DDERR_INVALIDPARAMS;
 
-    ddsd = *pDDSD;
+    ddsd.dwSize = sizeof(ddsd);
+    DD_STRUCT_COPY_BYSIZE((&ddsd),pDDSD);
     ddsd.dwFlags |= DDSD_HEIGHT | DDSD_WIDTH | DDSD_PITCH | DDSD_PIXELFORMAT;
     ddsd.dwHeight = This->height;
     ddsd.dwWidth = This->width;
@@ -438,7 +440,8 @@ create_offscreen(IDirectDrawImpl* This, LPDDSURFACEDESC2 pDDSD,
     if ((pDDSD->dwFlags&(DDSD_HEIGHT|DDSD_WIDTH)) != (DDSD_HEIGHT|DDSD_WIDTH))
 	return DDERR_INVALIDPARAMS;
 
-    ddsd = *pDDSD;
+    ddsd.dwSize = sizeof(ddsd);
+    DD_STRUCT_COPY_BYSIZE((&ddsd),pDDSD);
 
     if (!(ddsd.dwFlags & DDSD_PIXELFORMAT))
     {
diff --git a/dlls/ddraw/ddraw/thunks.c b/dlls/ddraw/ddraw/thunks.c
index bd800a9df2b..0136b73fde7 100644
--- a/dlls/ddraw/ddraw/thunks.c
+++ b/dlls/ddraw/ddraw/thunks.c
@@ -213,8 +213,6 @@ IDirectDraw2Impl_CreateSurface(LPDIRECTDRAW2 This, LPDDSURFACEDESC pSDesc,
     LPDIRECTDRAWSURFACE7 pSurface7;
     HRESULT hr;
 
-    /* the LPDDSURFACEDESC -> LPDDSURFACEDESC2 conversion should be ok, 
-     * since the data layout is the same */
     hr = IDirectDraw7_CreateSurface(COM_INTERFACE_CAST(IDirectDrawImpl,
 						       IDirectDraw2,
 						       IDirectDraw7,
@@ -235,13 +233,11 @@ IDirectDraw4Impl_CreateSurface(LPDIRECTDRAW4 This, LPDDSURFACEDESC2 pSDesc,
 			       LPDIRECTDRAWSURFACE4 *ppSurface,
 			       IUnknown *pUnkOuter)
 {
-    /* the LPDDSURFACEDESC -> LPDDSURFACEDESC2 conversion should be ok, 
-     * since the data layout is the same */
     return IDirectDraw7_CreateSurface(COM_INTERFACE_CAST(IDirectDrawImpl,
 							 IDirectDraw4,
 							 IDirectDraw7,
 							 This),
-				      (LPDDSURFACEDESC2)pSDesc,
+				      pSDesc,
 				      (LPDIRECTDRAWSURFACE7 *)ppSurface,
 				      pUnkOuter);
 }
diff --git a/dlls/ddraw/ddraw/user.c b/dlls/ddraw/ddraw/user.c
index 35f9f56128a..a6a823a0fa5 100644
--- a/dlls/ddraw/ddraw/user.c
+++ b/dlls/ddraw/ddraw/user.c
@@ -445,10 +445,10 @@ User_DirectDraw_GetCaps(LPDIRECTDRAW7 iface, LPDDCAPS pDriverCaps,
     }
 
     if (pDriverCaps != NULL)
-	memcpy(pDriverCaps, &caps, pDriverCaps->dwSize);
+	DD_STRUCT_COPY_BYSIZE(pDriverCaps,&caps);
 
     if (pHELCaps != NULL)
-	memcpy(pHELCaps, &caps, pHELCaps->dwSize);
+	DD_STRUCT_COPY_BYSIZE(pHELCaps,&caps);
 
     return DD_OK;
 }
diff --git a/dlls/ddraw/ddraw_private.h b/dlls/ddraw/ddraw_private.h
index 6bb896ff6fb..0a0e4b01978 100644
--- a/dlls/ddraw/ddraw_private.h
+++ b/dlls/ddraw/ddraw_private.h
@@ -21,9 +21,12 @@
 
 #define DD_STRUCT_COPY_BYSIZE(to,from)			\
 	do {						\
-	    	DWORD __size = to->dwSize;		\
-		memcpy(to,from,__size);			\
-		to->dwSize = __size;/*restore size*/	\
+	    	DWORD __size = (to)->dwSize;		\
+	    	DWORD __copysize = __size;		\
+	        if ((from)->dwSize < __size) 		\
+		    __copysize = (from)->dwSize;	\
+		memcpy(to,from,__copysize);		\
+		(to)->dwSize = __size;/*restore size*/	\
 	} while (0)
 
 /*****************************************************************************
diff --git a/dlls/ddraw/dsurface/main.c b/dlls/ddraw/dsurface/main.c
index eba0c93eb7b..a11785b284d 100644
--- a/dlls/ddraw/dsurface/main.c
+++ b/dlls/ddraw/dsurface/main.c
@@ -25,8 +25,10 @@ Main_DirectDrawSurface_Construct(IDirectDrawSurfaceImpl *This,
 				 IDirectDrawImpl *pDD,
 				 const DDSURFACEDESC2 *pDDSD)
 {
-    if (pDDSD != &This->surface_desc)
-	This->surface_desc = *pDDSD;
+    if (pDDSD != &This->surface_desc) {
+	This->surface_desc.dwSize = sizeof(This->surface_desc);
+	DD_STRUCT_COPY_BYSIZE(&(This->surface_desc),pDDSD);
+    }
     This->uniqueness_value = 1; /* unchecked */
     This->ref = 1;
 
@@ -680,7 +682,7 @@ Main_DirectDrawSurface_GetPixelFormat(LPDIRECTDRAWSURFACE7 iface,
     ICOM_THIS(IDirectDrawSurfaceImpl, iface);
 
     TRACE("(%p)->(%p)\n",This,pDDPixelFormat);
-    *pDDPixelFormat = This->surface_desc.u4.ddpfPixelFormat;
+    DD_STRUCT_COPY_BYSIZE(pDDPixelFormat,&This->surface_desc.u4.ddpfPixelFormat);
     return DD_OK;
 }
 
@@ -793,7 +795,8 @@ Main_DirectDrawSurface_Lock(LPDIRECTDRAWSURFACE7 iface, LPRECT prect,
 		 This,prect,pDDSD,flags,(DWORD)h);
 
     /* First, copy the Surface description */
-    memcpy(pDDSD, &(This->surface_desc), pDDSD->dwSize);
+    DD_STRUCT_COPY_BYSIZE(pDDSD,&(This->surface_desc));
+
     TRACE("locked surface: height=%ld, width=%ld, pitch=%ld\n",
 	  pDDSD->dwHeight,pDDSD->dwWidth,pDDSD->u1.lPitch);