diff --git a/Makefile.zarch b/Makefile.zarch
index b841d9b4d..092ca2589 100644
--- a/Makefile.zarch
+++ b/Makefile.zarch
@@ -12,5 +12,5 @@ endif
 # Enable floating-point expression contraction for clang, since it is the
 # default for gcc
 ifeq ($(C_COMPILER), CLANG)
-CCOMMON_OPT += -ffp-contract=fast
+CCOMMON_OPT += -ffp-contract=on
 endif