diff --git a/ports/atmel-samd/Makefile b/ports/atmel-samd/Makefile
index 008efb1483..249f003f9b 100755
--- a/ports/atmel-samd/Makefile
+++ b/ports/atmel-samd/Makefile
@@ -106,7 +106,7 @@ ifeq ($(DEBUG), 1)
   # Turn on Python modules useful for debugging (e.g. uheap, ustack).
   CFLAGS += -ggdb
   # You may want to disable -flto if it interferes with debugging.
-  #CFLAGS += -flto
+  CFLAGS += -flto
   # You may want to enable these flags to make setting breakpoints easier.
 ##   CFLAGS += -fno-inline -fno-ipa-sra
   ifeq ($(CHIP_FAMILY), samd21)