diff --git a/dlls/ntdll/env.c b/dlls/ntdll/env.c
index 821ffe49245..b8f537fd268 100644
--- a/dlls/ntdll/env.c
+++ b/dlls/ntdll/env.c
@@ -62,7 +62,7 @@ NTSTATUS WINAPI RtlCreateEnvironment(BOOLEAN inherit, PWSTR* env)
     }
     else 
     {
-        ULONG       size = 1;
+        SIZE_T      size = 1;
         PVOID       addr = NULL;
         nts = NtAllocateVirtualMemory(NtCurrentProcess(), &addr, 0, &size,
                                       MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
@@ -77,7 +77,7 @@ NTSTATUS WINAPI RtlCreateEnvironment(BOOLEAN inherit, PWSTR* env)
  */
 NTSTATUS WINAPI RtlDestroyEnvironment(PWSTR env) 
 {
-    ULONG size = 0;
+    SIZE_T size = 0;
 
     TRACE("(%p)!\n", env);
 
@@ -220,7 +220,7 @@ NTSTATUS WINAPI RtlSetEnvironmentVariable(PWSTR* penv, PUNICODE_STRING name,
     if ((old_size + len) * sizeof(WCHAR) > mbi.RegionSize)
     {
         LPWSTR  new_env;
-        ULONG   new_size = (old_size + len) * sizeof(WCHAR);
+        SIZE_T  new_size = (old_size + len) * sizeof(WCHAR);
 
         new_env = NULL;
         nts = NtAllocateVirtualMemory(NtCurrentProcess(), (void**)&new_env, 0,
@@ -422,7 +422,7 @@ NTSTATUS WINAPI RtlCreateProcessParameters( RTL_USER_PROCESS_PARAMETERS **result
     static const UNICODE_STRING null_str = { 0, 0, NULL };
 
     const RTL_USER_PROCESS_PARAMETERS *cur_params;
-    ULONG size, total_size;
+    SIZE_T size, total_size;
     void *ptr;
     NTSTATUS status;
 
@@ -482,6 +482,6 @@ NTSTATUS WINAPI RtlCreateProcessParameters( RTL_USER_PROCESS_PARAMETERS **result
 void WINAPI RtlDestroyProcessParameters( RTL_USER_PROCESS_PARAMETERS *params )
 {
     void *ptr = params;
-    ULONG size = 0;
+    SIZE_T size = 0;
     NtFreeVirtualMemory( NtCurrentProcess(), &ptr, &size, MEM_RELEASE );
 }
diff --git a/dlls/ntdll/handletable.c b/dlls/ntdll/handletable.c
index 7e0b41eb9bb..eb901ffb4aa 100644
--- a/dlls/ntdll/handletable.c
+++ b/dlls/ntdll/handletable.c
@@ -74,7 +74,7 @@ void WINAPI RtlInitializeHandleTable(ULONG MaxHandleCount, ULONG HandleSize, RTL
  */
 NTSTATUS WINAPI RtlDestroyHandleTable(RTL_HANDLE_TABLE * HandleTable)
 {
-    ULONG Size = 0;
+    SIZE_T Size = 0;
 
     TRACE("(%p)\n", HandleTable);
 
@@ -104,7 +104,7 @@ static NTSTATUS RtlpAllocateSomeHandles(RTL_HANDLE_TABLE * HandleTable)
     if (!HandleTable->FirstHandle)
     {
         PVOID FirstHandleAddr = NULL;
-        ULONG MaxSize = HandleTable->MaxHandleCount * HandleTable->HandleSize;
+        SIZE_T MaxSize = HandleTable->MaxHandleCount * HandleTable->HandleSize;
 
         /* reserve memory for the handles, but don't commit it yet because we
          * probably won't use most of it and it will use up physical memory */
@@ -123,8 +123,7 @@ static NTSTATUS RtlpAllocateSomeHandles(RTL_HANDLE_TABLE * HandleTable)
     }
     if (!HandleTable->NextFree)
     {
-        ULONG CommitSize = 4096; /* one page */
-        ULONG Offset;
+        SIZE_T Offset, CommitSize = 4096; /* one page */
         RTL_HANDLE * FreeHandle = NULL;
         PVOID NextAvailAddr = HandleTable->ReservedMemory;
 
diff --git a/dlls/ntdll/loader.c b/dlls/ntdll/loader.c
index 205fc006536..e305f2270e1 100644
--- a/dlls/ntdll/loader.c
+++ b/dlls/ntdll/loader.c
@@ -455,7 +455,7 @@ static WINE_MODREF *import_dll( HMODULE module, const IMAGE_IMPORT_DESCRIPTOR *d
     const char *name = get_rva( module, descr->Name );
     DWORD len = strlen(name) + 1;
     PVOID protect_base;
-    DWORD protect_size = 0;
+    SIZE_T protect_size = 0;
     DWORD protect_old;
 
     thunk_list = get_rva( module, (DWORD)descr->FirstThunk );
@@ -1287,7 +1287,7 @@ static NTSTATUS load_native_dll( LPCWSTR load_path, LPCWSTR name, HANDLE file,
     OBJECT_ATTRIBUTES attr;
     LARGE_INTEGER size;
     IMAGE_NT_HEADERS *nt;
-    DWORD len = 0;
+    SIZE_T len = 0;
     WINE_MODREF *wm;
     NTSTATUS status;
 
diff --git a/dlls/ntdll/server.c b/dlls/ntdll/server.c
index 8a6cd5d5552..6e82a05e176 100644
--- a/dlls/ntdll/server.c
+++ b/dlls/ntdll/server.c
@@ -126,7 +126,7 @@ static void fatal_perror( const char *err, ... )
 void server_exit_thread( int status )
 {
     struct wine_pthread_thread_info info;
-    ULONG size;
+    SIZE_T size;
 
     RtlAcquirePebLock();
     RemoveEntryList( &NtCurrentTeb()->TlsLinks );
diff --git a/dlls/ntdll/thread.c b/dlls/ntdll/thread.c
index a6b5d168bc4..f7dca185562 100644
--- a/dlls/ntdll/thread.c
+++ b/dlls/ntdll/thread.c
@@ -84,7 +84,7 @@ static inline NTSTATUS init_teb( TEB *teb )
  */
 static inline void free_teb( TEB *teb )
 {
-    ULONG size = 0;
+    SIZE_T size = 0;
     void *addr = teb;
     struct ntdll_thread_data *thread_data = (struct ntdll_thread_data *)teb->SystemReserved2;
 
@@ -105,7 +105,7 @@ void thread_init(void)
 {
     TEB *teb;
     void *addr;
-    ULONG info_size;
+    SIZE_T info_size;
     struct ntdll_thread_data *thread_data;
     struct wine_pthread_thread_info thread_info;
     static struct debug_info debug_info;  /* debug info for initial thread */
@@ -193,7 +193,7 @@ static void start_thread( struct wine_pthread_thread_info *info )
     PRTL_THREAD_START_ROUTINE func = startup_info->entry_point;
     void *arg = startup_info->entry_arg;
     struct debug_info debug_info;
-    ULONG size;
+    SIZE_T size;
 
     debug_info.str_pos = debug_info.strings;
     debug_info.out_pos = debug_info.output;
@@ -323,7 +323,7 @@ error:
     if (thread_data) wine_ldt_free_fs( thread_data->teb_sel );
     if (addr)
     {
-        ULONG size = 0;
+        SIZE_T size = 0;
         NtFreeVirtualMemory( NtCurrentProcess(), &addr, &size, MEM_RELEASE );
     }
     if (info) RtlFreeHeap( GetProcessHeap(), 0, info );