diff --git a/wordclock/Arduino.mk b/wordclock/Arduino.mk
index ba6289e..5b206ec 100644
--- a/wordclock/Arduino.mk
+++ b/wordclock/Arduino.mk
@@ -212,7 +212,8 @@ CPPFLAGS      = -mmcu=$(MCU) -DF_CPU=$(F_CPU) \
 			-I. -I$(ARDUINO_CORE_PATH) \
 			-I$(ARDUINO_VARIANT_PATH) \
 			$(SYS_INCLUDES) -g -Os -w -Wall \
-			-ffunction-sections -fdata-sections
+			-ffunction-sections -fdata-sections \
+			-Wall
 CFLAGS        = -std=gnu99
 CXXFLAGS      = -fno-exceptions
 ASFLAGS       = -mmcu=$(MCU) -I. -x assembler-with-cpp