diff --git a/src/hb-dsalgs.hh b/src/hb-dsalgs.hh
index 1d2f753c6..42fd7040f 100644
--- a/src/hb-dsalgs.hh
+++ b/src/hb-dsalgs.hh
@@ -42,8 +42,12 @@ struct hb_void_t { typedef void value; };
 template <typename T1, typename T2>
 struct hb_pair_t
 {
+  typedef hb_pair_t<T1, T2> pair_t;
+
   hb_pair_t (const T1& a, const T2& b) : first (a), second (b) {}
-  hb_pair_t (const hb_pair_t<T1, T2>& o) : hb_pair_t (o.first, o.second) {}
+  hb_pair_t (const pair_t& o) : hb_pair_t (o.first, o.second) {}
+
+  bool operator == (const pair_t& o) const { return first == o.first && second == o.second; }
 
   T1 first;
   T2 second;
diff --git a/src/hb-ot-layout-common.hh b/src/hb-ot-layout-common.hh
index b8ac7381c..0e626a447 100644
--- a/src/hb-ot-layout-common.hh
+++ b/src/hb-ot-layout-common.hh
@@ -1108,7 +1108,7 @@ struct Coverage
     hb_sorted_iter_t<Iter, const hb_pair_t<unsigned, hb_codepoint_t> >,
     hb_iter_mixin_t<Iter, const hb_pair_t<unsigned, hb_codepoint_t> >
   {
-    Iter (const Coverage &c_)
+    Iter (const Coverage &c_ = Null(Coverage))
     {
       memset (this, 0, sizeof (*this));
       format = c_.u.format;
@@ -1137,7 +1137,7 @@ struct Coverage
       default:			 break;
       }
     }
-    typedef hb_pair_t<unsigned, hb_codepoint_t> __item_type__;
+    typedef const hb_pair_t<unsigned, hb_codepoint_t> __item_type__;
     __item_type__ __item__ () const { return hb_pair (get_coverage (), get_glyph ()); }
 
     hb_codepoint_t get_glyph () const
@@ -1155,7 +1155,7 @@ struct Coverage
       {
       case 1: return u.format1.get_coverage ();
       case 2: return u.format2.get_coverage ();
-      default:return -1;
+      default:return NOT_COVERED;
       }
     }
 
diff --git a/src/test-iter.cc b/src/test-iter.cc
index 2e8c408dc..e0adb393f 100644
--- a/src/test-iter.cc
+++ b/src/test-iter.cc
@@ -29,6 +29,7 @@
 
 #include "hb-array.hh"
 #include "hb-set.hh"
+#include "hb-ot-layout-common.hh"
 
 
 template <typename T>
@@ -81,7 +82,7 @@ test_iterator (Iterator it)
 }
 
 template <typename Iterable> static void
-test_iterable (Iterable &lst = Null(Iterable))
+test_iterable (const Iterable &lst = Null(Iterable))
 {
   // Test that can take iterator from.
   test_iterator (lst.iter ());
@@ -112,5 +113,11 @@ main (int argc, char **argv)
   hb_sorted_array_t<int> sa;
   test_iterable (sa);
 
+  test_iterable<hb_array_t<int> > ();
+  test_iterable<hb_sorted_array_t<const int> > ();
+  test_iterable<hb_vector_t<float> > ();
+  test_iterable<hb_set_t> ();
+  test_iterable<OT::Coverage> ();
+
   return 0;
 }