diff --git a/src/ol/source/tilesource.js b/src/ol/source/tilesource.js
index bb7d3b0d96..98e6720dc8 100644
--- a/src/ol/source/tilesource.js
+++ b/src/ol/source/tilesource.js
@@ -75,12 +75,13 @@ ol.source.TileSource.prototype.findLoadedTiles = function(loadedTilesByZ, z,
   // FIXME this could be more efficient about filling partial holes
   var fullyCovered = true;
   var tile, tileCoord, tileCoordKey, x, y;
+  // TODO: tile range is misunderstood (inclusive or not?)
   for (x = tileRange.minX; x <= tileRange.maxX; ++x) {
     for (y = tileRange.minY; y <= tileRange.maxY; ++y) {
       tileCoord = new ol.TileCoord(z, x, y);
       tileCoordKey = tileCoord.toString();
       if (loadedTilesByZ[z] && loadedTilesByZ[z][tileCoordKey]) {
-        return false; // TODO: fix this
+        continue;
       }
       tile = this.getTile(tileCoord);
       if (!goog.isNull(tile) && tile.getState() == ol.TileState.LOADED) {
diff --git a/test/spec/ol/source/tilesource.test.js b/test/spec/ol/source/tilesource.test.js
index 9d51c59b04..f6639eaa69 100644
--- a/test/spec/ol/source/tilesource.test.js
+++ b/test/spec/ol/source/tilesource.test.js
@@ -30,8 +30,8 @@ describe('ol.source.TileSource', function() {
     it('adds loaded tiles to the lookup (z: 0)', function() {
       // a source with no loaded tiles
       var source = new ol.test.source.MockTileSource({
-        '0/0/-1': true,
-        '1/0/-1': true
+        '0/0/0': true,
+        '1/0/0': true
       });
 
       var loadedTilesByZ = {};
@@ -40,7 +40,7 @@ describe('ol.source.TileSource', function() {
       source.findLoadedTiles(loadedTilesByZ, 0, range);
       var keys = goog.object.getKeys(loadedTilesByZ);
       expect(keys.length).toBe(1);
-      var tile = loadedTilesByZ['0']['0/0/-1'];
+      var tile = loadedTilesByZ['0']['0/0/0'];
       expect(tile).toBeA(ol.Tile);
       expect(tile.state).toBe(ol.TileState.LOADED);
     });
@@ -48,8 +48,8 @@ describe('ol.source.TileSource', function() {
     it('adds loaded tiles to the lookup (z: 1)', function() {
       // a source with no loaded tiles
       var source = new ol.test.source.MockTileSource({
-        '0/0/-1': true,
-        '1/0/-1': true
+        '0/0/0': true,
+        '1/0/0': true
       });
 
       var loadedTilesByZ = {};
@@ -58,11 +58,100 @@ describe('ol.source.TileSource', function() {
       source.findLoadedTiles(loadedTilesByZ, 1, range);
       var keys = goog.object.getKeys(loadedTilesByZ);
       expect(keys.length).toBe(1);
-      var tile = loadedTilesByZ['1']['1/0/-1'];
+      var tile = loadedTilesByZ['1']['1/0/0'];
       expect(tile).toBeA(ol.Tile);
       expect(tile.state).toBe(ol.TileState.LOADED);
     });
 
+    it('returns true when all tiles are already loaded', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({
+        // TODO: tile range is misunderstood
+        '1/0/0': true,
+        '1/0/1': true,
+        '1/0/2': true,
+        '1/1/0': true,
+        '1/1/1': true,
+        '1/1/2': true,
+        '1/2/0': true,
+        '1/2/1': true,
+        '1/2/2': true,
+      });
+
+      var loadedTilesByZ = {};
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 1);
+      var allLoaded = source.findLoadedTiles(loadedTilesByZ, 1, range);
+      expect(allLoaded).toBe(true);
+    });
+
+    it('returns true when all tiles are already loaded (part 2)', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({});
+
+      var loadedTilesByZ = {
+        '1': {
+          '1/0/0': true,
+          '1/0/1': true,
+          '1/0/2': true,
+          '1/1/0': true,
+          '1/1/1': true,
+          '1/1/2': true,
+          '1/2/0': true,
+          '1/2/1': true,
+          '1/2/2': true,
+        }
+      };
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 1);
+      var allLoaded = source.findLoadedTiles(loadedTilesByZ, 1, range);
+      expect(allLoaded).toBe(true);
+    });
+
+    it('returns false when all tiles are already loaded', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({
+        '1/0/0': true,
+        '1/0/1': true,
+        '1/0/2': true,
+        '1/1/0': true,
+        '1/1/1': false,
+        '1/1/2': true,
+        '1/2/0': true,
+        '1/2/1': true,
+        '1/2/2': true,
+      });
+
+      var loadedTilesByZ = {};
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 1);
+      var allLoaded = source.findLoadedTiles(loadedTilesByZ, 1, range);
+      expect(allLoaded).toBe(false);
+    });
+
+    it('returns false when all tiles are already loaded (part 2)', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({});
+
+      var loadedTilesByZ = {
+        '1': {
+          '1/0/0': true,
+          '1/0/1': true,
+          '1/0/2': true,
+          '1/1/0': true,
+          '1/1/1': false,
+          '1/1/2': true,
+          '1/2/0': true,
+          '1/2/1': true,
+          '1/2/2': true,
+        }
+      };
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 1);
+      var allLoaded = source.findLoadedTiles(loadedTilesByZ, 1, range);
+      expect(allLoaded).toBe(false);
+    });
+
   });
 
 });
@@ -80,7 +169,7 @@ ol.test.source.MockTileSource = function(loaded) {
   var tileGrid = new ol.tilegrid.TileGrid({
     resolutions: [360 / 256, 180 / 256, 90 / 256, 45 / 256],
     extent: extent,
-    origin: new ol.Coordinate(-180, 180),
+    origin: new ol.Coordinate(-180, -180),
     tileSize: new ol.Size(256, 256)
   });
 
@@ -127,7 +216,7 @@ describe('ol.test.source.MockTileSource', function() {
     it('returns a tile with state based on constructor arg', function() {
       var source = new ol.test.source.MockTileSource({
         '0/0/0': true,
-        '1/0/-1': true
+        '1/0/0': true
       });
       var tile;
 
@@ -142,7 +231,7 @@ describe('ol.test.source.MockTileSource', function() {
       expect(tile.state).toBe(ol.TileState.IDLE);
 
       // check another loaded tile
-      tile = source.getTile(new ol.TileCoord(1, 0, -1));
+      tile = source.getTile(new ol.TileCoord(1, 0, 0));
       expect(tile).toBeA(ol.Tile);
       expect(tile.state).toBe(ol.TileState.LOADED);