diff --git a/libvips/include/vips/internal.h b/libvips/include/vips/internal.h
index 88bd7ea4..e9a78640 100644
--- a/libvips/include/vips/internal.h
+++ b/libvips/include/vips/internal.h
@@ -114,6 +114,7 @@ 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 59f4e95f..db931cb8 100644
--- a/libvips/iofuncs/init.c
+++ b/libvips/iofuncs/init.c
@@ -384,6 +384,7 @@ 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 4d57e9be..e7ae446d 100644
--- a/libvips/iofuncs/sinkscreen.c
+++ b/libvips/iofuncs/sinkscreen.c
@@ -1029,8 +1029,8 @@ render_thread_main( void *client )
 	return( NULL );
 }
 
-static void
-vips_sink_screen_init( void )
+void
+vips__sink_screen_init( void )
 {
 	g_assert( !render_thread ); 
 	g_assert( !render_dirty_lock ); 
@@ -1039,9 +1039,6 @@ vips_sink_screen_init( void )
 	render_thread = vips_g_thread_new( "sink_screen",
 		render_thread_main, NULL );
 	vips_semaphore_init( &n_render_dirty_sem, 0, "n_render_dirty" );
-
-	g_assert( render_thread ); 
-	g_assert( render_dirty_lock ); 
 }
 
 /**
@@ -1101,12 +1098,8 @@ 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, (GThreadFunc) vips_sink_screen_init, NULL );
-
 	if( tile_width <= 0 || tile_height <= 0 || 
 		max_tiles < -1 ) {
 		vips_error( "vips_sink_screen", "%s", _( "bad parameters" ) );