diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,7 @@
 BUILD_NUMBER ?= 0
 
 # SOURCES: list of sources in the user application
-SOURCES = main.c  adc.c gpio.c i2c.c interrupts.c uart.c  gps.c system_stm32f0xx.c system.c wspr.c
+SOURCES = main.c  adc.c gpio.c i2c.c interrupts.c uart.c  gps.c system_stm32f0xx.c system.c wspr.c rtc.c
 # TARGET: name of the user application
 TARGET = wsprhab-b$(BUILD_NUMBER)
 
@@ -38,11 +38,11 @@ JTENCODE_INCLUDES = -Ilib/jtencode
 
 # USER_CFLAGS: user C flags (enable warnings, enable debug info)
 USER_CFLAGS = -Wall -g -ffunction-sections -fdata-sections -Os -fno-common --function-sections -fdata-sections 
-#USER_CFLAGS += -flto
+USER_CFLAGS += -flto
 
 # USER_LDFLAGS:  user LD flags
 USER_LDFLAGS = -fno-exceptions -ffunction-sections -fdata-sections -Wl,--gc-sections 
-#USER_LDFLAGS += -flto
+USER_LDFLAGS += -flto
 USER_LDFLAGS += --static
 #USER_LDFLAGS += -nostartfiles