diff --git a/src/hb-map.hh b/src/hb-map.hh
index 84fe1d549..ab9c17eb1 100644
--- a/src/hb-map.hh
+++ b/src/hb-map.hh
@@ -140,9 +140,9 @@ struct hb_hashmap_t
     return true;
   }
 
-  void set (K key, V value)
+  bool set (K key, V value)
   {
-    set_with_hash (key, hb_hash (key), value);
+    return set_with_hash (key, hb_hash (key), value);
   }
 
   V get (K key) const
@@ -211,15 +211,15 @@ struct hb_hashmap_t
 
   protected:
 
-  void set_with_hash (K key, uint32_t hash, V value)
+  bool set_with_hash (K key, uint32_t hash, V value)
   {
-    if (unlikely (!successful)) return;
-    if (unlikely (key == kINVALID)) return;
-    if ((occupancy + occupancy / 2) >= mask && !resize ()) return;
+    if (unlikely (!successful)) return false;
+    if (unlikely (key == kINVALID)) return true;
+    if (unlikely ((occupancy + occupancy / 2) >= mask && !resize ())) return false;
     unsigned int i = bucket_for_hash (key, hash);
 
     if (value == vINVALID && items[i].key != key)
-      return; /* Trying to delete non-existent key. */
+      return true; /* Trying to delete non-existent key. */
 
     if (!items[i].is_unused ())
     {
@@ -235,6 +235,8 @@ struct hb_hashmap_t
     occupancy++;
     if (!items[i].is_tombstone ())
       population++;
+
+    return true;
   }
 
   unsigned int bucket_for (K key) const