diff --git a/hw/xbox/mcpx/nvnet/nvnet.c b/hw/xbox/mcpx/nvnet/nvnet.c
index 0a6bf219f5..c44ba307a3 100644
--- a/hw/xbox/mcpx/nvnet/nvnet.c
+++ b/hw/xbox/mcpx/nvnet/nvnet.c
@@ -558,8 +558,8 @@ static void nvnet_mmio_write(void *opaque, hwaddr addr,
     switch (addr) {
     case NVNET_RING_SIZE:
         nvnet_set_reg(s, addr, val, size);
-        s->rx_ring_size = ((val >> NVNET_RING_SIZE_RXSHIFT) & 0xffff) + 1;
-        s->tx_ring_size = ((val >> NVNET_RING_SIZE_TXSHIFT) & 0xffff) + 1;
+        s->rx_ring_size = GET_MASK(val, NVNET_RING_SIZE_RX) + 1;
+        s->tx_ring_size = GET_MASK(val, NVNET_RING_SIZE_TX) + 1;
         break;
 
     case NVNET_MII_CONTROL:
diff --git a/hw/xbox/mcpx/nvnet/nvnet_regs.h b/hw/xbox/mcpx/nvnet/nvnet_regs.h
index 2e46d36897..c9b54fae18 100644
--- a/hw/xbox/mcpx/nvnet/nvnet_regs.h
+++ b/hw/xbox/mcpx/nvnet/nvnet_regs.h
@@ -121,8 +121,8 @@
 #define NVNET_TX_RING_PHYS_ADDR                  0x100
 #define NVNET_RX_RING_PHYS_ADDR                  0x104
 #define NVNET_RING_SIZE                          0x108
-#  define NVNET_RING_SIZE_TXSHIFT                  0
-#  define NVNET_RING_SIZE_RXSHIFT                  16
+#  define NVNET_RING_SIZE_TX                       0x0000FFFF
+#  define NVNET_RING_SIZE_RX                       0xFFFF0000
 #define NVNET_UNKNOWN_TRANSMITTER_REG            0x10C
 #define NVNET_LINKSPEED                          0x110
 #  define NVNET_LINKSPEED_FORCE                    0x00010000