diff --git a/src/sync/ntapi_tt_sync_block.c b/src/sync/ntapi_tt_sync_block.c
index e52dd77..b28d56e 100644
--- a/src/sync/ntapi_tt_sync_block.c
+++ b/src/sync/ntapi_tt_sync_block.c
@@ -219,17 +219,20 @@ int32_t __stdcall __ntapi_tt_sync_block_server_lock(
 int32_t __stdcall __ntapi_tt_sync_block_unlock(
 	__in	nt_sync_block *	sync_block)
 {
-	int64_t cmp;
+	union {
+		int64_t			i64;
+		nt_large_integer	nti64;
+	} cmp;
 
 	if (sync_block->invalid)
 		return NT_STATUS_INVALID_HANDLE;
 
-	cmp = (int64_t)(pe_get_current_process_id()) << 32;
-	cmp += pe_get_current_thread_id();
+	cmp.nti64.ihigh = pe_get_current_process_id();
+	cmp.nti64.ulow  = pe_get_current_thread_id();
 
-	if (cmp != at_locked_cas_64(
+	if (cmp.i64 != at_locked_cas_64(
 			(int64_t *)&sync_block->tid,
-			cmp,0))
+			cmp.i64,0))
 		return NT_STATUS_RESOURCE_NOT_OWNED;
 
 	return NT_STATUS_SUCCESS;