diff --git a/lib/pixi/deepzoom/tile.js b/lib/pixi/deepzoom/tile.js
index eac6958..21186bb 100644
--- a/lib/pixi/deepzoom/tile.js
+++ b/lib/pixi/deepzoom/tile.js
@@ -6,6 +6,8 @@ const registeredTiles = new Map()
 let keepTextures = 0
 const keptTextures = []
 const lateTextures = new Map()
+let lastSweepTime = 0
+let sweepInterval = 2000.0
 
 /** The current Tile implementation simply uses PIXI.Sprites.
  *