diff --git a/boards/arcade_itsybitsy_m4/board_config.h b/boards/arcade_itsybitsy_m4/board_config.h
index 8f86b56f..1322d8ea 100644
--- a/boards/arcade_itsybitsy_m4/board_config.h
+++ b/boards/arcade_itsybitsy_m4/board_config.h
@@ -16,7 +16,7 @@
 #define BOARD_RGBLED_DATA_PIN PIN_PB03
 
 #define BOOT_USART_MODULE SERCOM3
-#define BOOT_USART_MASK APBAMASK
+#define BOOT_USART_MASK APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3 PINMUX_UNUSED
diff --git a/boards/circuitbrains_deluxe_m4/board_config.h b/boards/circuitbrains_deluxe_m4/board_config.h
index 326c6393..0103e2ef 100755
--- a/boards/circuitbrains_deluxe_m4/board_config.h
+++ b/boards/circuitbrains_deluxe_m4/board_config.h
@@ -13,7 +13,7 @@
 #define USB_PID 0xEC64
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/itsybitsy_m4/board_config.h b/boards/itsybitsy_m4/board_config.h
index a4f0ca1f..f603816e 100644
--- a/boards/itsybitsy_m4/board_config.h
+++ b/boards/itsybitsy_m4/board_config.h
@@ -18,7 +18,7 @@
 #define BOARD_RGBLED_DATA_PIN             PIN_PB03
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/metro_m4/board_config.h b/boards/metro_m4/board_config.h
index a8130d87..ae20abf3 100644
--- a/boards/metro_m4/board_config.h
+++ b/boards/metro_m4/board_config.h
@@ -18,7 +18,7 @@
 #define BOARD_NEOPIXEL_COUNT 1
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/metro_m4_airlift/board_config.h b/boards/metro_m4_airlift/board_config.h
index c8b0d723..ba44d0e1 100644
--- a/boards/metro_m4_airlift/board_config.h
+++ b/boards/metro_m4_airlift/board_config.h
@@ -18,7 +18,7 @@
 #define BOARD_NEOPIXEL_COUNT 1
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/mini_sam_m4/board_config.h b/boards/mini_sam_m4/board_config.h
index 796e4581..79fc3095 100644
--- a/boards/mini_sam_m4/board_config.h
+++ b/boards/mini_sam_m4/board_config.h
@@ -16,7 +16,7 @@
 #define BOARD_RGBLED_DATA_PIN             PIN_PB03
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/openbook_m4/board_config.h b/boards/openbook_m4/board_config.h
index ea918eac..180bb726 100644
--- a/boards/openbook_m4/board_config.h
+++ b/boards/openbook_m4/board_config.h
@@ -18,7 +18,7 @@
 #define BOARD_NEOPIXEL_COUNT 1
 
 #define BOOT_USART_MODULE                 SERCOM5
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBDMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBDMASK_SERCOM5
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/pewpew_m4/board_config.h b/boards/pewpew_m4/board_config.h
index da0652b7..b4bef4c2 100644
--- a/boards/pewpew_m4/board_config.h
+++ b/boards/pewpew_m4/board_config.h
@@ -15,7 +15,7 @@
 #define BOARD_SCREEN 1
 
 #define BOOT_USART_MODULE SERCOM3
-#define BOOT_USART_MASK APBAMASK
+#define BOOT_USART_MASK APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3 PINMUX_UNUSED
diff --git a/boards/pyportal_m4/board_config.h b/boards/pyportal_m4/board_config.h
index 85fdaf1e..5589dd22 100644
--- a/boards/pyportal_m4/board_config.h
+++ b/boards/pyportal_m4/board_config.h
@@ -18,7 +18,7 @@
 #define BOARD_NEOPIXEL_COUNT 1
 
 #define BOOT_USART_MODULE                 SERCOM5
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBDMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBDMASK_SERCOM5
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/sam32/board_config.h b/boards/sam32/board_config.h
index 6bfe5065..8934f6cd 100644
--- a/boards/sam32/board_config.h
+++ b/boards/sam32/board_config.h
@@ -16,7 +16,7 @@
 #define BOARD_NEOPIXEL_COUNT 1
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/trellis_m4/board_config.h b/boards/trellis_m4/board_config.h
index cc5abe53..81a78f55 100644
--- a/boards/trellis_m4/board_config.h
+++ b/boards/trellis_m4/board_config.h
@@ -16,7 +16,7 @@
 #define BOARD_RGBLED_DATA_PIN             PIN_PB03
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/uartlogger2/board_config.h b/boards/uartlogger2/board_config.h
index 3e4281b5..498009d4 100644
--- a/boards/uartlogger2/board_config.h
+++ b/boards/uartlogger2/board_config.h
@@ -18,7 +18,7 @@
 #define BOARD_NEOPIXEL_COUNT 1
 
 #define BOOT_USART_MODULE                 SERCOM3
-#define BOOT_USART_MASK                   APBAMASK
+#define BOOT_USART_MASK                   APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX        MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS           UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3                   PINMUX_UNUSED
diff --git a/boards/winterbloom_binary_star/board_config.h b/boards/winterbloom_binary_star/board_config.h
index c9735e4e..9a2b638e 100644
--- a/boards/winterbloom_binary_star/board_config.h
+++ b/boards/winterbloom_binary_star/board_config.h
@@ -17,7 +17,7 @@
 #define BOARD_RGBLED_DATA_PIN PIN_PA04
 
 #define BOOT_USART_MODULE SERCOM3
-#define BOOT_USART_MASK APBAMASK
+#define BOOT_USART_MASK APBBMASK
 #define BOOT_USART_BUS_CLOCK_INDEX MCLK_APBBMASK_SERCOM3
 #define BOOT_USART_PAD_SETTINGS UART_RX_PAD1_TX_PAD0
 #define BOOT_USART_PAD3 PINMUX_UNUSED