diff --git a/libvips/include/vips/internal.h b/libvips/include/vips/internal.h
index 84030580..d549c321 100644
--- a/libvips/include/vips/internal.h
+++ b/libvips/include/vips/internal.h
@@ -114,7 +114,6 @@ void vips__threadpool_init( void );
 
 void vips__cache_init( void );
 
-void vips__sink_screen_init( void );
 void vips__print_renders( void );
 
 void vips__type_leak( void );
diff --git a/libvips/iofuncs/init.c b/libvips/iofuncs/init.c
index 7c9cd5d9..aa1b5901 100644
--- a/libvips/iofuncs/init.c
+++ b/libvips/iofuncs/init.c
@@ -413,7 +413,6 @@ vips_init( const char *argv0 )
 #endif /*HAVE_THREAD_NEW*/
 
 	vips__threadpool_init();
-	vips__sink_screen_init();
 	vips__buffer_init();
 	vips__meta_init();
 
diff --git a/libvips/iofuncs/sinkscreen.c b/libvips/iofuncs/sinkscreen.c
index 9c216e59..c432cdcf 100644
--- a/libvips/iofuncs/sinkscreen.c
+++ b/libvips/iofuncs/sinkscreen.c
@@ -450,6 +450,9 @@ vips__render_shutdown( void )
 		}
 		else
 			g_mutex_unlock( render_dirty_lock );
+
+		VIPS_FREEF( vips_g_mutex_free, render_dirty_lock );
+		vips_semaphore_destroy( &n_render_dirty_sem );
 	}
 }
 
@@ -1027,8 +1030,8 @@ render_thread_main( void *client )
 	return( NULL );
 }
 
-void
-vips__sink_screen_init( void )
+static void *
+vips__sink_screen_init( void *data )
 {
 	g_assert( !render_thread ); 
 	g_assert( !render_dirty_lock ); 
@@ -1037,6 +1040,8 @@ vips__sink_screen_init( void )
 	vips_semaphore_init( &n_render_dirty_sem, 0, "n_render_dirty" );
 	render_thread = vips_g_thread_new( "sink_screen",
 		render_thread_main, NULL );
+
+	return( NULL );
 }
 
 /**
@@ -1096,8 +1101,12 @@ vips_sink_screen( VipsImage *in, VipsImage *out, VipsImage *mask,
 	int priority,
 	VipsSinkNotify notify_fn, void *a )
 {
+	static GOnce once = G_ONCE_INIT;
+
 	Render *render;
 
+	VIPS_ONCE( &once, vips__sink_screen_init, NULL );
+
 	if( tile_width <= 0 || tile_height <= 0 || 
 		max_tiles < -1 ) {
 		vips_error( "vips_sink_screen", "%s", _( "bad parameters" ) );