diff --git a/Makefile b/Makefile
index a216e69f6aa725a27bf44ff89bd8cf876759b561..1454638bbbec556594ca9aaec48c801bdf303e3a 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,7 @@ __pycache__:
 	py3compile -V 3.0- prime.py
 
 a.out:
-	gcc --std=c99 -Wall -lm prime.c
+	gcc --std=c99 -Wall -lm -O3 prime.c
 
 clean:
 	- rm -fr a.out __pycache__