diff --git a/src/hb-common.cc b/src/hb-common.cc
index 33a514d..9422555 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -363,8 +363,7 @@
 hb_user_data_array_t::set (hb_user_data_key_t *key,
 			   void *              data,
 			   hb_destroy_func_t   destroy,
-			   hb_bool_t           replace,
-			   hb_mutex_t         &lock)
+			   hb_bool_t           replace)
 {
   if (!key)
     return false;
@@ -382,20 +381,13 @@
 }
 
 void *
-hb_user_data_array_t::get (hb_user_data_key_t *key,
-			   hb_mutex_t         &lock)
+hb_user_data_array_t::get (hb_user_data_key_t *key)
 {
   hb_user_data_item_t item = {NULL };
 
   return items.find (key, &item, lock) ? item.data : NULL;
 }
 
-void
-hb_user_data_array_t::finish (hb_mutex_t &lock)
-{
-  items.finish (lock);
-}
-
 
 /* hb_version */
 
diff --git a/src/hb-object-private.hh b/src/hb-object-private.hh
index 0499226..8a9ae34 100644
--- a/src/hb-object-private.hh
+++ b/src/hb-object-private.hh
@@ -65,7 +65,7 @@
 
 /* user_data */
 
-#define HB_USER_DATA_ARRAY_INIT {HB_LOCKABLE_SET_INIT}
+#define HB_USER_DATA_ARRAY_INIT {HB_MUTEX_INIT, HB_LOCKABLE_SET_INIT}
 struct hb_user_data_array_t
 {
   /* TODO Add tracing. */
@@ -81,20 +81,19 @@
     void finish (void) { if (destroy) destroy (data); }
   };
 
+  hb_mutex_t lock;
   hb_lockable_set_t<hb_user_data_item_t, hb_mutex_t> items;
 
-  inline void init (void) { items.init (); }
+  inline void init (void) { lock.init (); items.init (); }
 
   HB_INTERNAL bool set (hb_user_data_key_t *key,
 			void *              data,
 			hb_destroy_func_t   destroy,
-			hb_bool_t           replace,
-			hb_mutex_t         &lock);
+			hb_bool_t           replace);
 
-  HB_INTERNAL void *get (hb_user_data_key_t *key,
-			hb_mutex_t          &lock);
+  HB_INTERNAL void *get (hb_user_data_key_t *key);
 
-  HB_INTERNAL void finish (hb_mutex_t &lock);
+  inline void finish (void) { items.finish (lock); lock.finish (); }
 };
 
 
@@ -103,10 +102,9 @@
 struct hb_object_header_t
 {
   hb_reference_count_t ref_count;
-  hb_mutex_t mutex;
   hb_user_data_array_t user_data;
 
-#define HB_OBJECT_HEADER_STATIC {HB_REFERENCE_COUNT_INVALID, HB_MUTEX_INIT, HB_USER_DATA_ARRAY_INIT}
+#define HB_OBJECT_HEADER_STATIC {HB_REFERENCE_COUNT_INVALID, HB_USER_DATA_ARRAY_INIT}
 
   static inline void *create (unsigned int size) {
     hb_object_header_t *obj = (hb_object_header_t *) calloc (1, size);
@@ -119,7 +117,6 @@
 
   inline void init (void) {
     ref_count.init (1);
-    mutex.init ();
     user_data.init ();
   }
 
@@ -140,8 +137,7 @@
       return false;
 
     ref_count.finish (); /* Do this before user_data */
-    user_data.finish (mutex);
-    mutex.finish ();
+    user_data.finish ();
 
     return true;
   }
@@ -153,14 +149,14 @@
     if (unlikely (!this || this->is_inert ()))
       return false;
 
-    return user_data.set (key, data, destroy_func, replace, mutex);
+    return user_data.set (key, data, destroy_func, replace);
   }
 
   inline void *get_user_data (hb_user_data_key_t *key) {
     if (unlikely (!this || this->is_inert ()))
       return NULL;
 
-    return user_data.get (key, mutex);
+    return user_data.get (key);
   }
 
   inline void trace (const char *function) const {