diff --git a/ports/atmel-samd/boards/pewpew10/mpconfigboard.h b/ports/atmel-samd/boards/pewpew10/mpconfigboard.h
index 6b3b4aa15c..2cb097e8dc 100644
--- a/ports/atmel-samd/boards/pewpew10/mpconfigboard.h
+++ b/ports/atmel-samd/boards/pewpew10/mpconfigboard.h
@@ -43,3 +43,5 @@
 
 #define DEFAULT_UART_BUS_RX (&pin_PA01)
 #define DEFAULT_UART_BUS_TX (&pin_PA00)
+
+#define SAMD21_BOD33_LEVEL (6)
diff --git a/ports/atmel-samd/boards/pewpew_m4/mpconfigboard.h b/ports/atmel-samd/boards/pewpew_m4/mpconfigboard.h
index 60cd8d754f..4b88c89f28 100644
--- a/ports/atmel-samd/boards/pewpew_m4/mpconfigboard.h
+++ b/ports/atmel-samd/boards/pewpew_m4/mpconfigboard.h
@@ -40,3 +40,5 @@
 #define IGNORE_PIN_PB09     1
 #define IGNORE_PIN_PB10     1
 #define IGNORE_PIN_PB11     1
+
+#define SAMD5x_E5x_BOD33_LEVEL (100)
diff --git a/ports/atmel-samd/mpconfigport.h b/ports/atmel-samd/mpconfigport.h
index 354097ce41..540a2f77c7 100644
--- a/ports/atmel-samd/mpconfigport.h
+++ b/ports/atmel-samd/mpconfigport.h
@@ -112,6 +112,14 @@
 #define CIRCUITPY_DEFAULT_STACK_SIZE                4096
 #endif
 
+#ifndef SAMD21_BOD33_LEVEL
+// Set brownout detection to ~2.7V. Default from factory is 1.7V,
+// which is too low for proper operation of external SPI flash chips
+// (they are 2.7-3.6V).
+#define SAMD21_BOD33_LEVEL (39)
+// 2.77V with hysteresis off. Table 37.20 in datasheet.
+#endif
+
 // Smallest unit of flash that can be erased.
 #define FLASH_ERASE_SIZE NVMCTRL_ROW_SIZE
 
@@ -129,6 +137,14 @@
 #define CIRCUITPY_DEFAULT_STACK_SIZE                (24*1024)
 #endif
 
+#ifndef SAMD5x_E5x_BOD33_LEVEL
+// Set brownout detection to ~2.7V. Default from factory is 1.7V,
+// which is too low for proper operation of external SPI flash chips
+// (they are 2.7-3.6V).
+#define SAMD5x_E5x_BOD33_LEVEL (200)
+// 2.7V: 1.5V + LEVEL * 6mV.
+#endif
+
 // Smallest unit of flash that can be erased.
 #define FLASH_ERASE_SIZE NVMCTRL_BLOCK_SIZE
 
diff --git a/ports/atmel-samd/supervisor/port.c b/ports/atmel-samd/supervisor/port.c
index e892e6cde5..65501861e0 100644
--- a/ports/atmel-samd/supervisor/port.c
+++ b/ports/atmel-samd/supervisor/port.c
@@ -206,11 +206,10 @@ static void rtc_init(void) {
 safe_mode_t port_init(void) {
 #if defined(SAMD21)
 
-    // Set brownout detection to ~2.7V. Default from factory is 1.7V,
-    // which is too low for proper operation of external SPI flash chips (they are 2.7-3.6V).
+    // Set brownout detection.
     // Disable while changing level.
     SYSCTRL->BOD33.bit.ENABLE = 0;
-    SYSCTRL->BOD33.bit.LEVEL = 39;  // 2.77V with hysteresis off. Table 37.20 in datasheet.
+    SYSCTRL->BOD33.bit.LEVEL = SAMD21_BOD33_LEVEL;
     SYSCTRL->BOD33.bit.ENABLE = 1;
 
     #ifdef ENABLE_MICRO_TRACE_BUFFER
@@ -225,11 +224,10 @@ safe_mode_t port_init(void) {
 #endif
 
 #if defined(SAM_D5X_E5X)
-    // Set brownout detection to ~2.7V. Default from factory is 1.7V,
-    // which is too low for proper operation of external SPI flash chips (they are 2.7-3.6V).
+    // Set brownout detection.
     // Disable while changing level.
     SUPC->BOD33.bit.ENABLE = 0;
-    SUPC->BOD33.bit.LEVEL = 200;  // 2.7V: 1.5V + LEVEL * 6mV.
+    SUPC->BOD33.bit.LEVEL = SAMD5x_E5x_BOD33_LEVEL;
     SUPC->BOD33.bit.ENABLE = 1;
 
     // MPU (Memory Protection Unit) setup.