diff --git a/autoconf/configure.ac b/autoconf/configure.ac
index 49a140cdc4a..3b4019658cc 100644
--- a/autoconf/configure.ac
+++ b/autoconf/configure.ac
@@ -728,6 +728,7 @@ AC_MSG_CHECKING([optimization flags])
 case "$withval" in
   default)
     case "$llvm_cv_os_type" in
+    FreeBSD) optimize_option=-O2 ;;
     MingW) optimize_option=-O2 ;;
     *)     optimize_option=-O3 ;;
     esac ;;