diff --git a/ports/atmel-samd/Makefile b/ports/atmel-samd/Makefile
index 721cfd4f0a..c828a78df5 100644
--- a/ports/atmel-samd/Makefile
+++ b/ports/atmel-samd/Makefile
@@ -94,14 +94,14 @@ endif
 
 ifeq ($(CHIP_FAMILY), samd51)
 PERIPHERALS_CHIP_FAMILY=sam_d5x_e5x
-OPTIMIZATION_FLAGS ?= -O2 -fno-inline-functions
+OPTIMIZATION_FLAGS ?= -Os
 # TinyUSB defines
 CFLAGS += -DCFG_TUSB_MCU=OPT_MCU_SAMD51 -DCFG_TUD_MIDI_RX_BUFSIZE=128 -DCFG_TUD_CDC_RX_BUFSIZE=256 -DCFG_TUD_MIDI_TX_BUFSIZE=128 -DCFG_TUD_CDC_TX_BUFSIZE=256 -DCFG_TUD_MSC_BUFSIZE=1024
 endif
 
 ifeq ($(CHIP_FAMILY), same51)
 PERIPHERALS_CHIP_FAMILY=sam_d5x_e5x
-OPTIMIZATION_FLAGS ?= -O2 -fno-inline-functions
+OPTIMIZATION_FLAGS ?= -Os
 # TinyUSB defines
 CFLAGS += -DCFG_TUSB_MCU=OPT_MCU_SAME5X -DCFG_TUD_MIDI_RX_BUFSIZE=128 -DCFG_TUD_CDC_RX_BUFSIZE=256 -DCFG_TUD_MIDI_TX_BUFSIZE=128 -DCFG_TUD_CDC_TX_BUFSIZE=256 -DCFG_TUD_MSC_BUFSIZE=1024
 endif