diff --git a/dlls/inetcomm/mimeole.c b/dlls/inetcomm/mimeole.c
index 94fb5589971..d63da8c8993 100644
--- a/dlls/inetcomm/mimeole.c
+++ b/dlls/inetcomm/mimeole.c
@@ -2821,7 +2821,7 @@ static ULONG WINAPI MimeAlloc_Release(
 
 static LPVOID WINAPI MimeAlloc_Alloc(
         IMimeAllocator* iface,
-        ULONG cb)
+        SIZE_T cb)
 {
     return CoTaskMemAlloc(cb);
 }
@@ -2829,7 +2829,7 @@ static LPVOID WINAPI MimeAlloc_Alloc(
 static LPVOID WINAPI MimeAlloc_Realloc(
         IMimeAllocator* iface,
         LPVOID pv,
-        ULONG cb)
+        SIZE_T cb)
 {
     return CoTaskMemRealloc(pv, cb);
 }
@@ -2841,7 +2841,7 @@ static void WINAPI MimeAlloc_Free(
     CoTaskMemFree(pv);
 }
 
-static ULONG WINAPI MimeAlloc_GetSize(
+static SIZE_T WINAPI MimeAlloc_GetSize(
         IMimeAllocator* iface,
         LPVOID pv)
 {
diff --git a/dlls/mapi32/imalloc.c b/dlls/mapi32/imalloc.c
index 90f29a10ee5..3e95a6c7cd3 100644
--- a/dlls/mapi32/imalloc.c
+++ b/dlls/mapi32/imalloc.c
@@ -112,9 +112,9 @@ static ULONG WINAPI IMAPIMalloc_fnRelease(LPMALLOC iface)
 /**************************************************************************
  * IMAPIMalloc_Alloc
  */
-static LPVOID WINAPI IMAPIMalloc_fnAlloc(LPMALLOC iface, DWORD cb)
+static LPVOID WINAPI IMAPIMalloc_fnAlloc(LPMALLOC iface, SIZE_T cb)
 {
-    TRACE("(%p)->(%d)\n", iface, cb);
+    TRACE("(%p)->(%ld)\n", iface, cb);
 
     return LocalAlloc(LMEM_FIXED, cb);
 }
@@ -122,9 +122,9 @@ static LPVOID WINAPI IMAPIMalloc_fnAlloc(LPMALLOC iface, DWORD cb)
 /**************************************************************************
  * IMAPIMalloc_Realloc
  */
-static LPVOID WINAPI IMAPIMalloc_fnRealloc(LPMALLOC iface, LPVOID pv, DWORD cb)
+static LPVOID WINAPI IMAPIMalloc_fnRealloc(LPMALLOC iface, LPVOID pv, SIZE_T cb)
 {
-    TRACE("(%p)->(%p, %d)\n", iface, pv, cb);
+    TRACE("(%p)->(%p, %ld)\n", iface, pv, cb);
 
     if (!pv)
         return LocalAlloc(LMEM_FIXED, cb);
@@ -148,7 +148,7 @@ static void WINAPI IMAPIMalloc_fnFree(LPMALLOC iface, LPVOID pv)
 /**************************************************************************
  * IMAPIMalloc_GetSize
  */
-static DWORD WINAPI IMAPIMalloc_fnGetSize(LPMALLOC iface, LPVOID pv)
+static SIZE_T WINAPI IMAPIMalloc_fnGetSize(LPMALLOC iface, LPVOID pv)
 {
     TRACE("(%p)->(%p)\n", iface, pv);
     return LocalSize(pv);
diff --git a/dlls/ole32/ifs.c b/dlls/ole32/ifs.c
index 18fd1fd58b2..6868897fd3b 100644
--- a/dlls/ole32/ifs.c
+++ b/dlls/ole32/ifs.c
@@ -143,8 +143,8 @@ static BOOL RemoveMemoryLocation(LPCVOID pMem)
 /******************************************************************************
  *	IMalloc32_QueryInterface	[VTABLE]
  */
-static HRESULT WINAPI IMalloc_fnQueryInterface(LPMALLOC iface,REFIID refiid,LPVOID *obj) {
-
+static HRESULT WINAPI IMalloc_fnQueryInterface(IMalloc *iface, REFIID refiid, void **obj)
+{
 	TRACE("(%s,%p)\n",debugstr_guid(refiid),obj);
 
 	if (IsEqualIID(&IID_IUnknown,refiid) || IsEqualIID(&IID_IMalloc,refiid)) {
@@ -157,21 +157,22 @@ static HRESULT WINAPI IMalloc_fnQueryInterface(LPMALLOC iface,REFIID refiid,LPVO
 /******************************************************************************
  *	IMalloc32_AddRefRelease		[VTABLE]
  */
-static ULONG WINAPI IMalloc_fnAddRefRelease (LPMALLOC iface) {
+static ULONG WINAPI IMalloc_fnAddRefRelease(IMalloc *iface)
+{
 	return 1;
 }
 
 /******************************************************************************
  *	IMalloc32_Alloc 		[VTABLE]
  */
-static LPVOID WINAPI IMalloc_fnAlloc(LPMALLOC iface, DWORD cb) {
+static void * WINAPI IMalloc_fnAlloc(IMalloc *iface, SIZE_T cb)
+{
+	void *addr;
 
-	LPVOID addr;
-
-	TRACE("(%d)\n",cb);
+	TRACE("(%ld)\n",cb);
 
 	if(Malloc32.pSpy) {
-	    DWORD preAllocResult;
+	    SIZE_T preAllocResult;
 	    
 	    EnterCriticalSection(&IMalloc32_SpyCS);
 	    preAllocResult = IMallocSpy_PreAlloc(Malloc32.pSpy, cb);
@@ -198,14 +199,14 @@ static LPVOID WINAPI IMalloc_fnAlloc(LPMALLOC iface, DWORD cb) {
 /******************************************************************************
  * IMalloc32_Realloc [VTABLE]
  */
-static LPVOID WINAPI IMalloc_fnRealloc(LPMALLOC iface,LPVOID pv,DWORD cb) {
+static void * WINAPI IMalloc_fnRealloc(IMalloc *iface, void *pv, SIZE_T cb)
+{
+	void *pNewMemory;
 
-	LPVOID pNewMemory;
-
-	TRACE("(%p,%d)\n",pv,cb);
+	TRACE("(%p,%ld)\n",pv,cb);
 
 	if(Malloc32.pSpy) {
-	    LPVOID pRealMemory;
+	    void *pRealMemory;
 	    BOOL fSpyed;
 
 	    EnterCriticalSection(&IMalloc32_SpyCS);
@@ -250,8 +251,8 @@ static LPVOID WINAPI IMalloc_fnRealloc(LPMALLOC iface,LPVOID pv,DWORD cb) {
 /******************************************************************************
  * IMalloc32_Free [VTABLE]
  */
-static VOID WINAPI IMalloc_fnFree(LPMALLOC iface,LPVOID pv) {
-
+static void WINAPI IMalloc_fnFree(IMalloc *iface, void *pv)
+{
         BOOL fSpyed = FALSE;
 
 	TRACE("(%p)\n",pv);
@@ -286,9 +287,9 @@ static VOID WINAPI IMalloc_fnFree(LPMALLOC iface,LPVOID pv) {
  *      win95:  size allocated (4 byte boundarys)
  *      win2k:  size originally requested !!! (allocated on 8 byte boundarys)
  */
-static DWORD WINAPI IMalloc_fnGetSize(LPMALLOC iface,LPVOID pv) {
-
-	DWORD cb;
+static SIZE_T WINAPI IMalloc_fnGetSize(IMalloc *iface, void *pv)
+{
+        SIZE_T cb;
         BOOL fSpyed = FALSE;
 
 	TRACE("(%p)\n",pv);
@@ -311,8 +312,8 @@ static DWORD WINAPI IMalloc_fnGetSize(LPMALLOC iface,LPVOID pv) {
 /******************************************************************************
  * IMalloc32_DidAlloc [VTABLE]
  */
-static INT WINAPI IMalloc_fnDidAlloc(LPMALLOC iface,LPVOID pv) {
-
+static INT WINAPI IMalloc_fnDidAlloc(IMalloc *iface, void *pv)
+{
         BOOL fSpyed = FALSE;
 	int didAlloc;
 
@@ -335,7 +336,8 @@ static INT WINAPI IMalloc_fnDidAlloc(LPMALLOC iface,LPVOID pv) {
 /******************************************************************************
  * IMalloc32_HeapMinimize [VTABLE]
  */
-static VOID WINAPI IMalloc_fnHeapMinimize(LPMALLOC iface) {
+static void WINAPI IMalloc_fnHeapMinimize(IMalloc *iface)
+{
 	TRACE("()\n");
 
 	if(Malloc32.pSpy) {
@@ -398,7 +400,7 @@ HRESULT WINAPI CoGetMalloc(DWORD context, IMalloc **imalloc)
  * 	Success: Pointer to newly allocated memory block.
  *  Failure: NULL.
  */
-LPVOID WINAPI CoTaskMemAlloc(ULONG size)
+LPVOID WINAPI CoTaskMemAlloc(SIZE_T size)
 {
         return IMalloc_Alloc(&Malloc32.IMalloc_iface,size);
 }
@@ -432,7 +434,7 @@ VOID WINAPI CoTaskMemFree(LPVOID ptr)
  * 	Success: Pointer to newly allocated memory block.
  *  Failure: NULL.
  */
-LPVOID WINAPI CoTaskMemRealloc(LPVOID pvOld, ULONG size)
+LPVOID WINAPI CoTaskMemRealloc(LPVOID pvOld, SIZE_T size)
 {
         return IMalloc_Realloc(&Malloc32.IMalloc_iface, pvOld, size);
 }
diff --git a/include/objbase.h b/include/objbase.h
index 23594ac1794..d73f220f02f 100644
--- a/include/objbase.h
+++ b/include/objbase.h
@@ -304,9 +304,9 @@ HRESULT WINAPI CoGetInstanceFromFile(COSERVERINFO* pServerInfo, CLSID* pClsid, I
 HRESULT WINAPI CoGetInstanceFromIStorage(COSERVERINFO* pServerInfo, CLSID* pClsid, IUnknown* punkOuter, DWORD dwClsCtx, IStorage* pstg, DWORD dwCount, MULTI_QI* pResults);
 
 HRESULT WINAPI CoGetMalloc(DWORD dwMemContext, LPMALLOC* lpMalloc);
-LPVOID WINAPI CoTaskMemAlloc(ULONG size) __WINE_ALLOC_SIZE(1);
+LPVOID WINAPI CoTaskMemAlloc(SIZE_T size) __WINE_ALLOC_SIZE(1);
 void WINAPI CoTaskMemFree(LPVOID ptr);
-LPVOID WINAPI CoTaskMemRealloc(LPVOID ptr, ULONG size);
+LPVOID WINAPI CoTaskMemRealloc(LPVOID ptr, SIZE_T size);
 
 HRESULT WINAPI CoRegisterMallocSpy(LPMALLOCSPY pMallocSpy);
 HRESULT WINAPI CoRevokeMallocSpy(void);
diff --git a/include/objidl.idl b/include/objidl.idl
index c18442fde1f..335282d74de 100644
--- a/include/objidl.idl
+++ b/include/objidl.idl
@@ -162,16 +162,16 @@ interface IMalloc : IUnknown
   typedef [unique] IMalloc *LPMALLOC;
 
   LPVOID Alloc(
-    [in] ULONG cb);
+    [in] SIZE_T cb);
 
   LPVOID Realloc(
     [in] LPVOID pv,
-    [in] ULONG cb);
+    [in] SIZE_T cb);
 
   void Free(
     [in] LPVOID pv);
 
-  ULONG GetSize(
+  SIZE_T GetSize(
     [in] LPVOID pv);
 
   int DidAlloc(LPVOID pv);
@@ -188,8 +188,8 @@ interface IMallocSpy : IUnknown
 {
   typedef [unique] IMallocSpy *LPMALLOCSPY;
 
-  ULONG PreAlloc(
-    [in] ULONG cbRequest);
+  SIZE_T PreAlloc(
+    [in] SIZE_T cbRequest);
 
   LPVOID PostAlloc(
     [in] LPVOID pActual);
@@ -201,9 +201,9 @@ interface IMallocSpy : IUnknown
   void PostFree(
     [in] BOOL fSpyed);
 
-  ULONG PreRealloc(
+  SIZE_T PreRealloc(
     [in] LPVOID pRequest,
-    [in] ULONG cbRequest,
+    [in] SIZE_T cbRequest,
     [out] LPVOID *ppNewRequest,
     [in] BOOL fSpyed);
 
@@ -215,8 +215,8 @@ interface IMallocSpy : IUnknown
     [in] LPVOID pRequest,
     [in] BOOL fSpyed);
 
-  ULONG PostGetSize(
-    [in] ULONG cbActual,
+  SIZE_T PostGetSize(
+    [in] SIZE_T cbActual,
     [in] BOOL fSpyed);
 
   LPVOID PreDidAlloc(