diff --git a/js/src/old-configure.in b/js/src/old-configure.in
index c50cbcb51be1..5a0d52f78e40 100644
--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -543,6 +543,15 @@ 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 -D_FORTIFY_SOURCE=2"
+   CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"
+   CXXFLAGS="$CXXFLAGS -D_FORTIFY_SOURCE=2"
+fi
+
 dnl ========================================================
 dnl System overrides of the defaults for target
 dnl ========================================================
diff --git a/old-configure.in b/old-configure.in
index 4bd33246c440..9a15fc663941 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -493,11 +493,19 @@ if test -n "$COMPILE_ENVIRONMENT"; then
    MOZ_CONFIG_SANITIZE
 fi
 
-# Add the hardening flags from moz.configure
+dnl ========================================================
+dnl Add optional and non-optional hardening flags
+dnl ========================================================
 CFLAGS="$CFLAGS $HARDENING_CFLAGS"
 CPPFLAGS="$CPPFLAGS $HARDENING_CFLAGS"
 CXXFLAGS="$CXXFLAGS $HARDENING_CFLAGS"
 
+if test "$GNU_CC" -o test -n "${CLANG_CC}${CLANG_CL}"; then
+   CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2"
+   CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"
+   CXXFLAGS="$CXXFLAGS -D_FORTIFY_SOURCE=2"
+fi
+
 dnl ========================================================
 dnl GNU specific defaults
 dnl ========================================================