diff --git a/ChangeLog b/ChangeLog
index 85751c41..08448e20 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 13/2/14 started 7.38.4
 - --sharpen=none option to vipsthumbnail was broken, thanks ferryfax
+- more locking on property create and lookup to help very-threaded systems,
+  thanks Nick 
 
 22/1/14 started 7.38.3
 - undeprecate VIPS_MASK_IDEAL_HIGHPASS and friends, ruby-vips was using them,
diff --git a/libvips/foreign/dzsave.c b/libvips/foreign/dzsave.c
index 6ec7b092..7f0ebeb0 100644
--- a/libvips/foreign/dzsave.c
+++ b/libvips/foreign/dzsave.c
@@ -36,9 +36,6 @@
  * 	- add --angle option
  * 19/6/13
  * 	- faster --centre logic, thanks Kacey
- * 25/6/13
- * 	- ping classes before starting workers, see comment below, thanks
- * 	  Kacey
  */
 
 /*
@@ -1170,37 +1167,6 @@ pyramid_strip( VipsRegion *region, VipsRect *area, void *a )
 	return( 0 );
 }
 
-static void *
-vips_class_ping( VipsObjectClass *class, void *dummy )
-{
-        return( NULL );
-}
-
-/* Loop over all classes. This will make sure they are all built.
- *
- * vips_dzsave() runs a set of pipelines from worker threads, and if the
- * operations it uses have not all been used previously, they can run their
- * class_init in parallel.
- *
- * This should be safe but seems not to be for reasons I don't understand.
- * For now, just ping all classes from the main thread before we set the
- * workers going. 
- *
- * This stops a crash on very many core machines, see
- *
- * https://github.com/jcupitt/libvips/issues/64
- */
-static void
-vips_class_ping_all( void )
-{
-	GType base;
-
-	if( !(base = g_type_from_name( "VipsObject" )) )
-		return;
-	vips_class_map_all( base, 
-		(VipsClassMapFn) vips_class_ping, NULL );
-}
-
 static int
 vips_foreign_save_dz_build( VipsObject *object )
 {
@@ -1328,10 +1294,6 @@ vips_foreign_save_dz_build( VipsObject *object )
 	if( pyramid_mkdir( dz ) )
 		return( -1 );
 
-	/* Build all vips classes, see comment above. 
-	 */
-	vips_class_ping_all();
-
 	if( vips_sink_disc( save->ready, pyramid_strip, dz ) )
 		return( -1 );
 
diff --git a/libvips/iofuncs/object.c b/libvips/iofuncs/object.c
index bb93e76f..99837b28 100644
--- a/libvips/iofuncs/object.c
+++ b/libvips/iofuncs/object.c
@@ -349,7 +349,13 @@ vips_argument_instance_free( VipsArgumentInstance *argument_instance )
 VipsArgument *
 vips__argument_table_lookup( VipsArgumentTable *table, GParamSpec *pspec )
 {
-	return( g_hash_table_lookup( table, pspec ) );
+	VipsArgument *argument;
+
+	g_mutex_lock( vips__global_lock );
+	argument = (VipsArgument *) g_hash_table_lookup( table, pspec );
+	g_mutex_unlock( vips__global_lock );
+
+	return( argument );
 }
 
 static void
@@ -1400,6 +1406,7 @@ vips_object_class_install_argument( VipsObjectClass *object_class,
 	GParamSpec *pspec, VipsArgumentFlags flags, int priority, guint offset )
 {
 	VipsArgumentClass *argument_class = g_new( VipsArgumentClass, 1 );
+	GSList *argument_table_traverse;
 
 #ifdef DEBUG
 	printf( "vips_object_class_install_argument: %p %s %s\n", 
@@ -1408,10 +1415,13 @@ vips_object_class_install_argument( VipsObjectClass *object_class,
 		g_param_spec_get_name( pspec ) );
 #endif /*DEBUG*/
 
+	/* object_class->argument* is shared, so we must lock.
+	 */
+	g_mutex_lock( vips__global_lock );
+
 	/* Must be a new one.
 	 */
-	g_assert( !vips__argument_table_lookup( object_class->argument_table,
-		pspec ) );
+	g_assert( !g_hash_table_lookup( object_class->argument_table, pspec ) );
 
 	/* Mustn't have INPUT and OUTPUT both set.
 	 */
@@ -1444,10 +1454,21 @@ vips_object_class_install_argument( VipsObjectClass *object_class,
 			G_TYPE_FROM_CLASS( object_class );
 	}
 
-	object_class->argument_table_traverse = g_slist_prepend(
-		object_class->argument_table_traverse, argument_class );
-	object_class->argument_table_traverse = g_slist_sort(
-		object_class->argument_table_traverse, traverse_sort );
+	/* We read argument_table_traverse without a lock (eg. see 
+	 * vips_argument_map()), so we must be very careful updating it.
+	 */
+	argument_table_traverse = 
+		g_slist_copy( object_class->argument_table_traverse );
+
+	argument_table_traverse = g_slist_prepend(
+		argument_table_traverse, argument_class );
+	argument_table_traverse = g_slist_sort(
+		argument_table_traverse, traverse_sort );
+	VIPS_SWAP( GSList *, 
+		argument_table_traverse, 
+		object_class->argument_table_traverse ); 
+
+	g_slist_free( argument_table_traverse );  
 
 #ifdef DEBUG
 {
@@ -1467,6 +1488,8 @@ vips_object_class_install_argument( VipsObjectClass *object_class,
 	}
 }
 #endif /*DEBUG*/
+
+	g_mutex_unlock( vips__global_lock );
 }
 
 static void