diff --git a/ports/samd/Makefile b/ports/samd/Makefile
index ff1701374a..2f90836d57 100644
--- a/ports/samd/Makefile
+++ b/ports/samd/Makefile
@@ -52,9 +52,7 @@ PIN_AF_TABLE_CSV = mcu/$(MCU_SERIES_LOWER)/pin-af-table.csv
 BOARD_PINS = $(BOARD_DIR)/pins.csv
 GEN_PIN_AF = pin_af_table.c
 
-CFLAGS_MCU_SAMD21 = -mtune=cortex-m0plus -mcpu=cortex-m0plus -msoft-float
-CFLAGS_MCU_SAMD51 = -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard
-CFLAGS += $(INC) -Wall -Werror -std=c99 -nostdlib -mthumb $(CFLAGS_MCU_$(MCU_SERIES)) -fsingle-precision-constant -Wdouble-promotion
+CFLAGS += $(INC) -Wall -Werror -std=c99 -nostdlib -mthumb $(CFLAGS_MCU) -fsingle-precision-constant -Wdouble-promotion
 CFLAGS += -DMCU_$(MCU_SERIES) -D__$(CMSIS_MCU)__
 CFLAGS += $(CFLAGS_EXTRA)
 
diff --git a/ports/samd/mcu/samd21/mpconfigmcu.mk b/ports/samd/mcu/samd21/mpconfigmcu.mk
index 287d6d18be..5f003e470d 100644
--- a/ports/samd/mcu/samd21/mpconfigmcu.mk
+++ b/ports/samd/mcu/samd21/mpconfigmcu.mk
@@ -1,3 +1,5 @@
+CFLAGS_MCU += -mtune=cortex-m0plus -mcpu=cortex-m0plus -msoft-float
+
 SRC_S += shared/runtime/gchelper_m0.s
 
 LIBM_SRC_C +=  $(addprefix lib/libm/,\
diff --git a/ports/samd/mcu/samd51/mpconfigmcu.mk b/ports/samd/mcu/samd51/mpconfigmcu.mk
index a016ba0a7f..b8fe5dd24a 100644
--- a/ports/samd/mcu/samd51/mpconfigmcu.mk
+++ b/ports/samd/mcu/samd51/mpconfigmcu.mk
@@ -1,3 +1,5 @@
+CFLAGS_MCU += -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard
+
 MICROPY_VFS_LFS2 ?= 1
 MICROPY_VFS_FAT ?= 1
 FROZEN_MANIFEST ?= mcu/$(MCU_SERIES_LOWER)/manifest.py