diff --git a/hardware/arduino/avr/boards.txt b/hardware/arduino/avr/boards.txt
index b6d742589..85a9bf382 100644
--- a/hardware/arduino/avr/boards.txt
+++ b/hardware/arduino/avr/boards.txt
@@ -20,7 +20,6 @@ uno.build.mcu=atmega328p
 uno.build.f_cpu=16000000L
 uno.build.core=arduino
 uno.build.variant=standard
-uno.build.extra_flags=
 
 ##############################################################
 
diff --git a/hardware/arduino/avr/platform.txt b/hardware/arduino/avr/platform.txt
index f3f45bd72..557b2d3af 100644
--- a/hardware/arduino/avr/platform.txt
+++ b/hardware/arduino/avr/platform.txt
@@ -20,6 +20,8 @@ compiler.elf2hex.flags=-O ihex -R .eeprom
 compiler.elf2hex.cmd=avr-objcopy
 compiler.ldflags=
 compiler.size.cmd=avr-size
+# this can be overriden in boards.txt
+build.extra_flags=
 
 # AVR compile patterns
 # --------------------
diff --git a/hardware/arduino/sam/platform.txt b/hardware/arduino/sam/platform.txt
index b76258243..78ded36ae 100644
--- a/hardware/arduino/sam/platform.txt
+++ b/hardware/arduino/sam/platform.txt
@@ -21,6 +21,9 @@ compiler.elf2hex.cmd=arm-none-eabi-objcopy
 compiler.ldflags=
 compiler.size.cmd=arm-none-eabi-size
 compiler.define=-DARDUINO=
+# this can be overriden in boards.txt
+build.extra_flags=
+
 
 compiler.libsam.c.flags="-I{build.system.path}/libsam" "-I{build.system.path}/CMSIS/CMSIS/Include/" "-I{build.system.path}/CMSIS/Device/ATMEL/"