diff --git a/build/ck.build.s390x b/build/ck.build.s390x
index 5abec30..2a91187 100644
--- a/build/ck.build.s390x
+++ b/build/ck.build.s390x
@@ -1 +1 @@
-CFLAGS+=-O2
+CFLAGS+=-O2 -D__s390x__