#define N_ROUND_UP(x,s) \
(((ULONG)(x)+(s)-1) & ~((ULONG)(s)-1))
-//
-// Maximum message size that can be sent through an LPC Port without a section
-//
-#define PORT_MAXIMUM_MESSAGE_LENGTH 256
-
//
// Port Object Access Masks
//
#ifdef NTOS_MODE_USER
+//
+// Maximum message size that can be sent through an LPC Port without a section
+//
+#ifdef _WIN64
+#define PORT_MAXIMUM_MESSAGE_LENGTH 512
+#else
+#define PORT_MAXIMUM_MESSAGE_LENGTH 256
+#endif
+
//
// Portable LPC Types for 32/64-bit compatibility
//