diff --git a/Makefile b/Makefile
index 871a04e..a1ec0cb 100644
--- a/Makefile
+++ b/Makefile
@@ -23,7 +23,7 @@ ASFLAGS  = -march=rv32i -mabi=ilp32
 LD       = $(TARGET)-gcc
 LDFLAGS  = -march=rv32i -mabi=ilp32 -Wl,-Tprogmem.lds -ffreestanding -nostartfiles
 CC       = $(TARGET)-gcc
-CFLAGS   = -march=rv32i -mabi=ilp32 -Wall -Wextra -pedantic -DFREQ=$(FREQ_PLL)000000 -Os
+CFLAGS   = -march=rv32i -mabi=ilp32 -Wall -Wextra -pedantic -DFREQ=$(FREQ_PLL)000000 -O2
 OBJCOPY  = $(TARGET)-objcopy
 
 .PHONY: all clean syntax time stat flash