diff --git a/src/hb-algs.hh b/src/hb-algs.hh
index b4e79e8abcdbd61f54fe21fbbb74be5b37901860..85f4f56d51e256ff1ea44000d859048cfff40fb2 100644
--- a/src/hb-algs.hh
+++ b/src/hb-algs.hh
@@ -35,7 +35,7 @@ template <typename T>
 inline typename T::iter_t
 hb_iter (const T& c) { return c.iter (); }
 
-static HB_UNUSED struct hb_identity_t
+static HB_UNUSED const struct hb_identity_t
 {
   template <typename T> T
   operator () (const T& v) const { return v; }
@@ -59,13 +59,13 @@ struct hb_pair_t
 template <typename T1, typename T2> static inline hb_pair_t<T1, T2>
 hb_pair (T1 a, T2 b) { return hb_pair_t<T1, T2> (a, b); }
 
-static HB_UNUSED struct hb_first_t
+static HB_UNUSED const struct hb_first_t
 {
   template <typename Pair> typename Pair::first_t
   operator () (const Pair& pair) const { return pair.first; }
 } hb_first;
 
-static HB_UNUSED struct hb_second_t
+static HB_UNUSED const struct hb_second_t
 {
   template <typename Pair> typename Pair::second_t
   operator () (const Pair& pair) const { return pair.second; }
diff --git a/src/hb-iter.hh b/src/hb-iter.hh
index b538ddf02c250a16548a15304987f82141d45a29..da93a5b3749037237bee0c458546ab2ab58815d8 100644
--- a/src/hb-iter.hh
+++ b/src/hb-iter.hh
@@ -280,7 +280,7 @@ struct hb_filter_iter_factory_t
   Pred p;
   Proj f;
 };
-template <typename Pred, typename Proj = hb_identity_t&>
+template <typename Pred, typename Proj = const hb_identity_t&>
 inline hb_filter_iter_factory_t<Pred, Proj>
 hb_filter (Pred&& p, Proj&& f = hb_identity)
 { return hb_filter_iter_factory_t<Pred, Proj> (p, f); }