diff --git a/dlls/d3d8/buffer.c b/dlls/d3d8/buffer.c
index cd68f6cc231..f10ec68413b 100644
--- a/dlls/d3d8/buffer.c
+++ b/dlls/d3d8/buffer.c
@@ -300,7 +300,7 @@ HRESULT vertexbuffer_init(IDirect3DVertexBuffer8Impl *buffer, IDirect3DDevice8Im
 
 static inline IDirect3DIndexBuffer8Impl *impl_from_IDirect3DIndexBuffer8(IDirect3DIndexBuffer8 *iface)
 {
-    return CONTAINING_RECORD(iface, IDirect3DIndexBuffer8Impl, lpVtbl);
+    return CONTAINING_RECORD(iface, IDirect3DIndexBuffer8Impl, IDirect3DIndexBuffer8_iface);
 }
 
 static HRESULT WINAPI d3d8_indexbuffer_QueryInterface(IDirect3DIndexBuffer8 *iface, REFIID riid, void **object)
@@ -324,7 +324,7 @@ static HRESULT WINAPI d3d8_indexbuffer_QueryInterface(IDirect3DIndexBuffer8 *ifa
 
 static ULONG WINAPI d3d8_indexbuffer_AddRef(IDirect3DIndexBuffer8 *iface)
 {
-    IDirect3DIndexBuffer8Impl *buffer = (IDirect3DIndexBuffer8Impl *)iface;
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
     ULONG refcount = InterlockedIncrement(&buffer->ref);
 
     TRACE("%p increasing refcount to %u.\n", iface, refcount);
@@ -342,7 +342,7 @@ static ULONG WINAPI d3d8_indexbuffer_AddRef(IDirect3DIndexBuffer8 *iface)
 
 static ULONG WINAPI d3d8_indexbuffer_Release(IDirect3DIndexBuffer8 *iface)
 {
-    IDirect3DIndexBuffer8Impl *buffer = (IDirect3DIndexBuffer8Impl *)iface;
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
     ULONG refcount = InterlockedDecrement(&buffer->ref);
 
     TRACE("%p decreasing refcount to %u.\n", iface, refcount);
@@ -362,11 +362,14 @@ static ULONG WINAPI d3d8_indexbuffer_Release(IDirect3DIndexBuffer8 *iface)
     return refcount;
 }
 
-static HRESULT WINAPI d3d8_indexbuffer_GetDevice(IDirect3DIndexBuffer8 *iface, IDirect3DDevice8 **device)
+static HRESULT WINAPI d3d8_indexbuffer_GetDevice(IDirect3DIndexBuffer8 *iface,
+        IDirect3DDevice8 **device)
 {
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
+
     TRACE("iface %p, device %p.\n", iface, device);
 
-    *device = (IDirect3DDevice8 *)((IDirect3DIndexBuffer8Impl *)iface)->parentDevice;
+    *device = buffer->parentDevice;
     IDirect3DDevice8_AddRef(*device);
 
     TRACE("Returning device %p.\n", *device);
@@ -428,12 +431,13 @@ static HRESULT WINAPI d3d8_indexbuffer_FreePrivateData(IDirect3DIndexBuffer8 *if
 
 static DWORD WINAPI d3d8_indexbuffer_SetPriority(IDirect3DIndexBuffer8 *iface, DWORD priority)
 {
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
     DWORD previous;
 
     TRACE("iface %p, priority %u.\n", iface, priority);
 
     wined3d_mutex_lock();
-    previous = wined3d_buffer_set_priority(((IDirect3DIndexBuffer8Impl *)iface)->wineD3DIndexBuffer, priority);
+    previous = wined3d_buffer_set_priority(buffer->wineD3DIndexBuffer, priority);
     wined3d_mutex_unlock();
 
     return previous;
@@ -441,12 +445,13 @@ static DWORD WINAPI d3d8_indexbuffer_SetPriority(IDirect3DIndexBuffer8 *iface, D
 
 static DWORD WINAPI d3d8_indexbuffer_GetPriority(IDirect3DIndexBuffer8 *iface)
 {
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
     DWORD priority;
 
     TRACE("iface %p.\n", iface);
 
     wined3d_mutex_lock();
-    priority = wined3d_buffer_get_priority(((IDirect3DIndexBuffer8Impl *)iface)->wineD3DIndexBuffer);
+    priority = wined3d_buffer_get_priority(buffer->wineD3DIndexBuffer);
     wined3d_mutex_unlock();
 
     return priority;
@@ -454,10 +459,12 @@ static DWORD WINAPI d3d8_indexbuffer_GetPriority(IDirect3DIndexBuffer8 *iface)
 
 static void WINAPI d3d8_indexbuffer_PreLoad(IDirect3DIndexBuffer8 *iface)
 {
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
+
     TRACE("iface %p.\n", iface);
 
     wined3d_mutex_lock();
-    wined3d_buffer_preload(((IDirect3DIndexBuffer8Impl *)iface)->wineD3DIndexBuffer);
+    wined3d_buffer_preload(buffer->wineD3DIndexBuffer);
     wined3d_mutex_unlock();
 }
 
@@ -468,17 +475,17 @@ static D3DRESOURCETYPE WINAPI d3d8_indexbuffer_GetType(IDirect3DIndexBuffer8 *if
     return D3DRTYPE_INDEXBUFFER;
 }
 
-static HRESULT WINAPI d3d8_indexbuffer_Lock(IDirect3DIndexBuffer8 *iface,
-        UINT offset, UINT size, BYTE **data, DWORD flags)
+static HRESULT WINAPI d3d8_indexbuffer_Lock(IDirect3DIndexBuffer8 *iface, UINT offset, UINT size,
+        BYTE **data, DWORD flags)
 {
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
     HRESULT hr;
 
     TRACE("iface %p, offset %u, size %u, data %p, flags %#x.\n",
             iface, offset, size, data, flags);
 
     wined3d_mutex_lock();
-    hr = wined3d_buffer_map(((IDirect3DIndexBuffer8Impl *)iface)->wineD3DIndexBuffer,
-            offset, size, data, flags);
+    hr = wined3d_buffer_map(buffer->wineD3DIndexBuffer, offset, size, data, flags);
     wined3d_mutex_unlock();
 
     return hr;
@@ -486,18 +493,21 @@ static HRESULT WINAPI d3d8_indexbuffer_Lock(IDirect3DIndexBuffer8 *iface,
 
 static HRESULT WINAPI d3d8_indexbuffer_Unlock(IDirect3DIndexBuffer8 *iface)
 {
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
+
     TRACE("iface %p.\n", iface);
 
     wined3d_mutex_lock();
-    wined3d_buffer_unmap(((IDirect3DIndexBuffer8Impl *)iface)->wineD3DIndexBuffer);
+    wined3d_buffer_unmap(buffer->wineD3DIndexBuffer);
     wined3d_mutex_unlock();
 
     return D3D_OK;
 }
 
-static HRESULT WINAPI d3d8_indexbuffer_GetDesc(IDirect3DIndexBuffer8 *iface, D3DINDEXBUFFER_DESC *desc)
+static HRESULT WINAPI d3d8_indexbuffer_GetDesc(IDirect3DIndexBuffer8 *iface,
+        D3DINDEXBUFFER_DESC *desc)
 {
-    IDirect3DIndexBuffer8Impl *buffer = (IDirect3DIndexBuffer8Impl *)iface;
+    IDirect3DIndexBuffer8Impl *buffer = impl_from_IDirect3DIndexBuffer8(iface);
     struct wined3d_resource_desc wined3d_desc;
     struct wined3d_resource *wined3d_resource;
 
@@ -553,7 +563,7 @@ HRESULT indexbuffer_init(IDirect3DIndexBuffer8Impl *buffer, IDirect3DDevice8Impl
 {
     HRESULT hr;
 
-    buffer->lpVtbl = &d3d8_indexbuffer_vtbl;
+    buffer->IDirect3DIndexBuffer8_iface.lpVtbl = &d3d8_indexbuffer_vtbl;
     buffer->ref = 1;
     buffer->format = wined3dformat_from_d3dformat(format);
 
diff --git a/dlls/d3d8/d3d8_private.h b/dlls/d3d8/d3d8_private.h
index e84b60acd7c..6ec67126005 100644
--- a/dlls/d3d8/d3d8_private.h
+++ b/dlls/d3d8/d3d8_private.h
@@ -287,10 +287,8 @@ HRESULT vertexbuffer_init(IDirect3DVertexBuffer8Impl *buffer, IDirect3DDevice8Im
  */
 struct IDirect3DIndexBuffer8Impl
 {
-    /* IUnknown fields */
-    const IDirect3DIndexBuffer8Vtbl *lpVtbl;
-    LONG                             ref;
-
+    IDirect3DIndexBuffer8 IDirect3DIndexBuffer8_iface;
+    LONG ref;
     struct wined3d_buffer *wineD3DIndexBuffer;
     IDirect3DDevice8 *parentDevice;
     enum wined3d_format_id format;
diff --git a/dlls/d3d8/device.c b/dlls/d3d8/device.c
index adae05ed7c0..3537cb7fb26 100644
--- a/dlls/d3d8/device.c
+++ b/dlls/d3d8/device.c
@@ -870,7 +870,7 @@ static HRESULT WINAPI IDirect3DDevice8Impl_CreateIndexBuffer(IDirect3DDevice8 *i
     }
 
     TRACE("Created index buffer %p.\n", object);
-    *buffer = (IDirect3DIndexBuffer8 *)object;
+    *buffer = &object->IDirect3DIndexBuffer8_iface;
 
     return D3D_OK;
 }