diff --git a/src/hb-bit-set-invertible.hh b/src/hb-bit-set-invertible.hh
index 2ec1c8fbe..18b80b5bb 100644
--- a/src/hb-bit-set-invertible.hh
+++ b/src/hb-bit-set-invertible.hh
@@ -56,6 +56,7 @@ struct hb_bit_set_invertible_t
   bool in_error () const { return s.in_error (); }
   explicit operator bool () const { return !is_empty (); }
 
+  void alloc (unsigned sz) { s.alloc (sz); }
   void reset ()
   {
     s.reset ();
diff --git a/src/hb-bit-set.hh b/src/hb-bit-set.hh
index f20014576..e98e7377a 100644
--- a/src/hb-bit-set.hh
+++ b/src/hb-bit-set.hh
@@ -97,6 +97,13 @@ struct hb_bit_set_t
     return true;
   }
 
+  void alloc (unsigned sz)
+  {
+    sz >>= (page_t::PAGE_BITS_LOG_2 - 1);
+    pages.alloc (sz);
+    page_map.alloc (sz);
+  }
+
   void reset ()
   {
     successful = true;
diff --git a/src/hb-set.hh b/src/hb-set.hh
index 9eacaf4f6..18274b2f2 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh
@@ -77,6 +77,7 @@ struct hb_sparseset_t
   void err () { s.err (); }
   bool in_error () const { return s.in_error (); }
 
+  void alloc (unsigned sz) { s.alloc (sz); }
   void reset () { s.reset (); }
   void clear () { s.clear (); }
   void invert () { s.invert (); }