diff --git a/src/resize.cc b/src/resize.cc
index 2a5e3c08..0e1993be 100755
--- a/src/resize.cc
+++ b/src/resize.cc
@@ -934,8 +934,7 @@ class ResizeWorker : public NanAsyncWorker {
         baton->outputFormat = "tiff";
       } else if (outputDz) {
         // Write DZ to file
-        std::string filename_no_extension = baton->output.substr(0, baton->output.length() - 4);
-        if (vips_dzsave(image, filename_no_extension.c_str(), "strip", !baton->withMetadata,
+        if (vips_dzsave(image, baton->output.c_str(), "strip", !baton->withMetadata,
             "tile_size", baton->tileSize, "overlap", baton->tileOverlap, NULL)) {
           return Error();
         }
diff --git a/test/unit/tile.js b/test/unit/tile.js
index f109ba7a..46bce654 100755
--- a/test/unit/tile.js
+++ b/test/unit/tile.js
@@ -177,9 +177,9 @@ describe('Tile', function() {
     describe('Deep Zoom output', function() {
 
       it('Tile size - 256px default', function(done) {
-        var directory = fixtures.path('output256_files');
+        var directory = fixtures.path('output.256_files');
         rimraf(directory, function() {
-          sharp(fixtures.inputJpg).toFile(fixtures.path('output256.dzi'), function(err, info) {
+          sharp(fixtures.inputJpg).toFile(fixtures.path('output.256.dzi'), function(err, info) {
             if (err) throw err;
             assert.strictEqual('dz', info.format);
             assertDeepZoomTiles(directory, 256, 13, done);
@@ -188,9 +188,9 @@ describe('Tile', function() {
       });
 
       it('Tile size/overlap - 512/16px', function(done) {
-        var directory = fixtures.path('output512_files');
+        var directory = fixtures.path('output.512_files');
         rimraf(directory, function() {
-          sharp(fixtures.inputJpg).tile(512, 16).toFile(fixtures.path('output512.dzi'), function(err, info) {
+          sharp(fixtures.inputJpg).tile(512, 16).toFile(fixtures.path('output.512.dzi'), function(err, info) {
             if (err) throw err;
             assert.strictEqual('dz', info.format);
             assertDeepZoomTiles(directory, 512 + 2 * 16, 13, done);