diff --git a/2019/karns/Makefile b/2019/karns/Makefile
index ae573279e..9287751fb 100644
--- a/2019/karns/Makefile
+++ b/2019/karns/Makefile
@@ -130,7 +130,7 @@ ALT_TARGET=
 ############################
 # FORCE no -O level        #
 # ##########################
-COPT+= -O0
+OPT+= -O0
 
 #################
 # build the entry