--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -539,16 +539,25 @@ case "$host" in
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
     HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 esac
 
 MOZ_DOING_LTO(lto_is_enabled)
 
 dnl ========================================================
+dnl Add optional and non-optional hardening flags
+dnl ========================================================
+if test "$GNU_CC" -o test -n "${CLANG_CC}${CLANG_CL}"; then
+   CFLAGS="$CFLAGS $HARDENING_CFLAGS -D_FORTIFY_SOURCE=2"
+   CPPFLAGS="$CPPFLAGS $HARDENING_CFLAGS -D_FORTIFY_SOURCE=2"
+   CXXFLAGS="$CXXFLAGS $HARDENING_CFLAGS -D_FORTIFY_SOURCE=2"
+fi
+
+dnl ========================================================
 dnl System overrides of the defaults for target
 dnl ========================================================
 
 case "$target" in
 *-darwin*)
     MKSHLIB='$(CXX) $(CXXFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MKCSHLIB='$(CC) $(CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MOZ_OPTIMIZE_FLAGS="-O3 -fno-stack-protector"