diff --git a/dlls/pstorec/pstorec.c b/dlls/pstorec/pstorec.c
index 493501f10a5..b2e729babda 100644
--- a/dlls/pstorec/pstorec.c
+++ b/dlls/pstorec/pstorec.c
@@ -33,10 +33,15 @@ WINE_DEFAULT_DEBUG_CHANNEL(pstores);
 
 typedef struct
 {
-    const IPStoreVtbl *lpVtbl;
+    IPStore IPStore_iface;
     LONG ref;
 } PStore_impl;
 
+static inline PStore_impl *impl_from_IPStore(IPStore *iface)
+{
+    return CONTAINING_RECORD(iface, PStore_impl, IPStore_iface);
+}
+
 BOOL WINAPI DllMain(HINSTANCE hinst, DWORD fdwReason, LPVOID fImpLoad)
 {
     TRACE("%p %x %p\n", hinst, fdwReason, fImpLoad);
@@ -62,7 +67,7 @@ static HRESULT WINAPI PStore_fnQueryInterface(
         REFIID riid,
         LPVOID *ppvObj)
 {
-    PStore_impl *This = (PStore_impl *)iface;
+    PStore_impl *This = impl_from_IPStore(iface);
 
     TRACE("%p %s\n",This,debugstr_guid(riid));
 
@@ -87,7 +92,7 @@ static HRESULT WINAPI PStore_fnQueryInterface(
  */
 static ULONG WINAPI PStore_fnAddRef(IPStore* iface)
 {
-    PStore_impl *This = (PStore_impl *)iface;
+    PStore_impl *This = impl_from_IPStore(iface);
 
     TRACE("%p %u\n", This, This->ref);
 
@@ -99,7 +104,7 @@ static ULONG WINAPI PStore_fnAddRef(IPStore* iface)
  */
 static ULONG WINAPI PStore_fnRelease(IPStore* iface)
 {
-    PStore_impl *This = (PStore_impl *)iface;
+    PStore_impl *This = impl_from_IPStore(iface);
     LONG ref;
 
     TRACE("%p %u\n", This, This->ref);
@@ -359,7 +364,7 @@ HRESULT WINAPI PStoreCreateInstance( IPStore** ppProvider,
     if( !ips )
         return E_OUTOFMEMORY;
 
-    ips->lpVtbl = &pstores_vtbl;
+    ips->IPStore_iface.lpVtbl = &pstores_vtbl;
     ips->ref = 1;
 
     *ppProvider = (IPStore*) ips;