diff --git a/cpu/samd21/Makefile.include b/cpu/samd21/Makefile.include
index 46dcfe3720961c435b17743b570394dcd95bffd3..ab5f80f11d4c49451a77578132e7c3c9cd8dc891 100644
--- a/cpu/samd21/Makefile.include
+++ b/cpu/samd21/Makefile.include
@@ -6,7 +6,4 @@ export CFLAGS += -DDONT_USE_CMSIS_INIT
 # use the hwtimer compatibility layer
 USEMODULE += hwtimer_compat
 
-# TODO: remove once the CPU implementation is stable with -Os
-CFLAGS_OPT = -O0
-
 include $(RIOTCPU)/Makefile.include.cortexm_common