diff --git a/ports/atmel-samd/Makefile b/ports/atmel-samd/Makefile
index 20c79de8f1..72c7d96882 100644
--- a/ports/atmel-samd/Makefile
+++ b/ports/atmel-samd/Makefile
@@ -148,7 +148,7 @@ else
   endif
 endif
 
-CFLAGS += $(INC) -Wall -Werror -std=gnu11 -nostdlib -fshort-enums $(BASE_CFLAGS) $(CFLAGS_MOD) $(COPT) -Wimplicit-fallthrough=2
+CFLAGS += $(INC) -Wall -Werror -std=gnu11 -nostdlib -fshort-enums $(BASE_CFLAGS) $(CFLAGS_MOD) $(COPT)
 
 ifeq ($(CHIP_FAMILY), samd21)
 CFLAGS += \
diff --git a/py/circuitpy_defns.mk b/py/circuitpy_defns.mk
index 04e38d81ea..0e87287c13 100644
--- a/py/circuitpy_defns.mk
+++ b/py/circuitpy_defns.mk
@@ -31,6 +31,7 @@ BASE_CFLAGS = \
 	-fsingle-precision-constant \
 	-fno-strict-aliasing \
 	-Wdouble-promotion \
+	-Wimplicit-fallthrough=2 \
 	-Wno-endif-labels \
 	-Wstrict-prototypes \
 	-Werror-implicit-function-declaration \