diff --git a/ports/stm32/eth.c b/ports/stm32/eth.c
index cece15d457..81faca5cb4 100644
--- a/ports/stm32/eth.c
+++ b/ports/stm32/eth.c
@@ -133,12 +133,14 @@ typedef struct _eth_dma_t {
     eth_dma_tx_descr_t tx_descr[TX_BUF_NUM];
     uint8_t rx_buf[RX_BUF_NUM * RX_BUF_SIZE] __attribute__((aligned(8)));
     uint8_t tx_buf[TX_BUF_NUM * TX_BUF_SIZE] __attribute__((aligned(8)));
+    #if !defined(STM32H5) && !defined(STM32N6)
     // Make sure the size of this struct is 16k, for the MPU.
     uint8_t padding[16 * 1024
                     - sizeof(eth_dma_rx_descr_t) * RX_BUF_NUM
                     - sizeof(eth_dma_tx_descr_t) * TX_BUF_NUM
                     - RX_BUF_NUM * RX_BUF_SIZE
                     - TX_BUF_NUM * TX_BUF_SIZE];
+    #endif
 } eth_dma_t;
 
 typedef struct _eth_t {
@@ -220,8 +222,6 @@ uint32_t eth_phy_read(uint32_t phy_addr, uint32_t reg) {
 }
 
 int eth_init(eth_t *self, int mac_idx, uint32_t phy_addr, int phy_type) {
-    MP_STATIC_ASSERT(sizeof(eth_dma_t) == 16 * 1024);
-
     mp_hal_get_mac(mac_idx, &self->netif.hwaddr[0]);
     self->netif.hwaddr_len = 6;
     self->phy_addr = phy_addr;
@@ -295,8 +295,9 @@ static int eth_mac_init(eth_t *self) {
     // Configure MPU
     uint32_t irq_state = mpu_config_start();
     #if defined(STM32H5) || defined(STM32N6)
-    mpu_config_region(MPU_REGION_ETH, (uint32_t)&eth_dma, MPU_CONFIG_ETH(16 * 1024));
+    mpu_config_region(MPU_REGION_ETH, (uint32_t)&eth_dma, MPU_CONFIG_ETH(sizeof(eth_dma_t)));
     #else
+    MP_STATIC_ASSERT(sizeof(eth_dma_t) == 16 * 1024);
     mpu_config_region(MPU_REGION_ETH, (uint32_t)&eth_dma, MPU_CONFIG_ETH(MPU_REGION_SIZE_16KB));
     #endif
     mpu_config_end(irq_state);