diff --git a/src/source/image_source.js b/src/source/image_source.js
index fa889ff7146..d8252e07889 100644
--- a/src/source/image_source.js
+++ b/src/source/image_source.js
@@ -91,7 +91,7 @@ class ImageSource extends Evented implements Source {
 
         this.url = this.options.url;
 
-        ajax.getImage(this.map._transformRequest(this.url), (err, image) => {
+        ajax.getImage(this.map._transformRequest(this.url, ajax.ResourceType.Image), (err, image) => {
             if (err) {
                 this.fire('error', {error: err});
             } else if (image) {
diff --git a/src/source/raster_tile_source.js b/src/source/raster_tile_source.js
index 94a3916f10e..b930fea0e39 100644
--- a/src/source/raster_tile_source.js
+++ b/src/source/raster_tile_source.js
@@ -52,7 +52,7 @@ class RasterTileSource extends Evented implements Source {
 
     load() {
         this.fire('dataloading', {dataType: 'source'});
-        loadTileJSON(this._options, (url) => { return this.map._transformRequest(url); }, (err, tileJSON) => {
+        loadTileJSON(this._options, (url) => { return this.map._transformRequest(url, ajax.ResourceType.Source); }, (err, tileJSON) => {
             if (err) {
                 this.fire('error', err);
             } else if (tileJSON) {
@@ -91,7 +91,7 @@ class RasterTileSource extends Evented implements Source {
     loadTile(tile: Tile, callback: Callback<void>) {
         const url = normalizeURL(tile.coord.url(this.tiles, null, this.scheme), this.url, this.tileSize);
 
-        tile.request = ajax.getImage(this.map._transformRequest(url), (err, img) => {
+        tile.request = ajax.getImage(this.map._transformRequest(url, ajax.ResourceType.Tile), (err, img) => {
             delete tile.request;
 
             if (tile.aborted) {
diff --git a/src/source/vector_tile_source.js b/src/source/vector_tile_source.js
index fc6d035d03e..e6c2b1deacc 100644
--- a/src/source/vector_tile_source.js
+++ b/src/source/vector_tile_source.js
@@ -5,6 +5,7 @@ const util = require('../util/util');
 const loadTileJSON = require('./load_tilejson');
 const normalizeURL = require('../util/mapbox').normalizeTileURL;
 const TileBounds = require('./tile_bounds');
+const ResourceType = require('../util/ajax').ResourceType;
 
 import type {Source} from './source';
 import type TileCoord from './tile_coord';
@@ -56,7 +57,7 @@ class VectorTileSource extends Evented implements Source {
     load() {
         this.fire('dataloading', {dataType: 'source'});
 
-        loadTileJSON(this._options, (url) => { return this.map._transformRequest(url); }, (err, tileJSON) => {
+        loadTileJSON(this._options, (url) => { return this.map._transformRequest(url, ResourceType.Source); }, (err, tileJSON) => {
             if (err) {
                 this.fire('error', err);
             } else if (tileJSON) {
@@ -96,7 +97,7 @@ class VectorTileSource extends Evented implements Source {
         const overscaling = tile.coord.z > this.maxzoom ? Math.pow(2, tile.coord.z - this.maxzoom) : 1;
         const url = normalizeURL(tile.coord.url(this.tiles, this.maxzoom, this.scheme), this.url);
         const params = {
-            request: this.map._transformRequest(url),
+            request: this.map._transformRequest(url, ResourceType.Tile),
             uid: tile.uid,
             coord: tile.coord,
             zoom: tile.coord.z,
diff --git a/src/style/image_sprite.js b/src/style/image_sprite.js
index 30f98a1eeaa..bf80583da6b 100644
--- a/src/style/image_sprite.js
+++ b/src/style/image_sprite.js
@@ -39,7 +39,7 @@ class ImageSprite extends Evented {
 
         const format = this.retina ? '@2x' : '';
         let url = normalizeURL(base, format, '.json');
-        const jsonRequest = transformRequestCallback ? transformRequestCallback(url) : { url: url};
+        const jsonRequest = transformRequestCallback ? transformRequestCallback(url, ajax.ResourceType.SpriteJSON) : { url: url};
         ajax.getJSON(jsonRequest, (err, data) => {
             if (err) {
                 this.fire('error', {error: err});
@@ -49,7 +49,7 @@ class ImageSprite extends Evented {
             }
         });
         url = normalizeURL(base, format, '.png');
-        const imageRequest = transformRequestCallback ? transformRequestCallback(url) : { url: url};
+        const imageRequest = transformRequestCallback ? transformRequestCallback(url, ajax.ResourceType.SpriteImage) : { url: url};
         ajax.getImage(imageRequest, (err, img) => {
             if (err) {
                 this.fire('error', {error: err});
diff --git a/src/style/style.js b/src/style/style.js
index a36ad2dcdc9..e981efff4eb 100644
--- a/src/style/style.js
+++ b/src/style/style.js
@@ -85,8 +85,8 @@ class Style extends Evented {
             }
         });
 
-        const transformRequest = (url) => {
-            return  this.map ? this.map._transformRequest(url) : { url: url};
+        const transformRequest = (url, resourceType) => {
+            return  this.map ? this.map._transformRequest(url, resourceType) : { url: url};
         };
 
         const stylesheetLoaded = (err, stylesheet) => {
@@ -117,7 +117,7 @@ class Style extends Evented {
         };
 
         if (typeof stylesheet === 'string') {
-            ajax.getJSON(transformRequest(mapbox.normalizeStyleURL(stylesheet)), stylesheetLoaded);
+            ajax.getJSON(transformRequest(mapbox.normalizeStyleURL(stylesheet), ajax.ResourceType.Style), stylesheetLoaded);
         } else {
             browser.frame(stylesheetLoaded.bind(this, null, stylesheet));
         }
diff --git a/src/symbol/glyph_source.js b/src/symbol/glyph_source.js
index 40cd3597c9a..303763804d1 100644
--- a/src/symbol/glyph_source.js
+++ b/src/symbol/glyph_source.js
@@ -149,7 +149,7 @@ class GlyphSource extends Evented {
     }
 
     loadPBF(url, callback) {
-        const request  = this.transformRequestCallback ? this.transformRequestCallback(url) : { url: url };
+        const request  = this.transformRequestCallback ? this.transformRequestCallback(url, ajax.ResourceType.Glyphs) : { url: url };
         ajax.getArrayBuffer(request, callback);
     }
 
diff --git a/src/ui/map.js b/src/ui/map.js
index 4bd35b59736..8d9e7152585 100755
--- a/src/ui/map.js
+++ b/src/ui/map.js
@@ -34,6 +34,8 @@ type IControl = {
 }
 /* eslint-enable no-use-before-define */
 
+type ResourceTypeEnum = $Keys<typeof ajax.ResourceType>;
+
 type MapOptions = {
     hash?: boolean,
     interactive?: boolean,
@@ -608,7 +610,7 @@ class Map extends Camera {
     /**
      * @private
      */
-    _transformRequest(url: string): RequestParameters {
+    _transformRequest(url: string, resourceType?: ResourceTypeEnum): RequestParameters {
         let requestParameters: RequestParameters = {
             url: url,
             headers: {}
@@ -618,7 +620,7 @@ class Map extends Camera {
             return requestParameters;
         }
 
-        requestParameters = this._transformRequestCallback(url) || requestParameters;
+        requestParameters = this._transformRequestCallback(url, resourceType || ajax.ResourceType.Unknown) || requestParameters;
         return requestParameters;
     }
 
@@ -629,8 +631,8 @@ class Map extends Camera {
      * @function setRequestTransform
      * @param {Function} callback Callback function called with the requested URL. Return an object with a transformed URL and headers (optional)
      * @example
-     * Map.setRequestTransform( (url)=> {
-     *  if(url.startsWith('http://myHost') {
+     * Map.setRequestTransform( (url, resourceType)=> {
+     *  if(resourceType == 'Source' && url.startsWith('http://myHost') {
      *   return {
      *    url: url.replace('http', 'https'),
      *    headers: { 'withCredentials': true}
@@ -1180,7 +1182,7 @@ class Map extends Camera {
      * @see [Add an icon to the map](https://www.mapbox.com/mapbox-gl-js/example/add-image/)
      */
     loadImage(url: string, callback: Function) {
-        ajax.getImage(this._transformRequest(url), callback);
+        ajax.getImage(this._transformRequest(url, ajax.ResourceType.Image), callback);
     }
 
     /**
diff --git a/src/util/ajax.js b/src/util/ajax.js
index c084e35c384..51cfa1f5c2f 100644
--- a/src/util/ajax.js
+++ b/src/util/ajax.js
@@ -5,18 +5,17 @@ const window = require('./window');
 /**
  * The type of a resource.
  */
-// type ResourceType = "Unknown" | "Style" | "Source" | "Tile" | "Glyphs" | "SpriteImage" | "SpriteJSON" | "Image";
-// TODO: AHM:
 const ResourceType = {
-    Unknown: Symbol('Unknown'),
-    Style: Symbol('Style'),
-    Source: Symbol('Source'),
-    Tile: Symbol('Tile'),
-    Glyphs: Symbol('Glyphs'),
-    SpriteImage: Symbol('SpriteImage'),
-    SpriteJSON: Symbol('SpriteJSON'),
-    Image: Symbol('Image')
+    Unknown: 'Unknown',
+    Style: 'Style',
+    Source: 'Source',
+    Tile: 'Tile',
+    Glyphs: 'Glyphs',
+    SpriteImage: 'SpriteImage',
+    SpriteJSON: 'SpriteJSON',
+    Image: 'Image'
 };
+exports.ResourceType = ResourceType;
 
 if (typeof Object.freeze == 'function') {
     Object.freeze(ResourceType);
@@ -27,12 +26,10 @@ if (typeof Object.freeze == 'function') {
  * @typedef {Object} RequestParameters
  * @property {string} url The URL to be requested.
  * @property {Object} headers The headers to be sent with the request.
- * @property {Boolean} withCredentials Whether cross-site requests should be made with cookies.
+ * @property {boolean} withCredentials Whether cross-site requests should be made with cookies.
  */
 export type RequestParameters = {
     url: string,
-    // TODO: AHM:
-    // resourceType?: ResourceType,
     headers?: Object,
     withCredentials? : Boolean
 };
diff --git a/test/unit/source/image_source.test.js b/test/unit/source/image_source.test.js
index 239ad104649..5b9bd5949c6 100644
--- a/test/unit/source/image_source.test.js
+++ b/test/unit/source/image_source.test.js
@@ -56,6 +56,7 @@ test('ImageSource', (t) => {
         source.onAdd(map);
         t.ok(spy.calledOnce);
         t.equal(spy.getCall(0).args[0], '/image.png');
+        t.equal(spy.getCall(0).args[1], 'Image');
         t.end();
     });
 
diff --git a/test/unit/source/raster_tile_source.test.js b/test/unit/source/raster_tile_source.test.js
index 104c6fe780a..41587fbeb1e 100644
--- a/test/unit/source/raster_tile_source.test.js
+++ b/test/unit/source/raster_tile_source.test.js
@@ -37,14 +37,15 @@ test('RasterTileSource', (t) => {
             tiles: ["http://example.com/{z}/{x}/{y}.png"],
             bounds: [-47, -7, -45, -5]
         }));
-        const spy = t.spy((e) => {
+        const transformSpy = t.spy((e) => {
             return { url: e };
         });
 
-        createSource({ url: "/source.json" }, spy);
+        createSource({ url: "/source.json" }, transformSpy);
         window.server.respond();
 
-        t.ok(spy.calledWith('/source.json'));
+        t.equal(transformSpy.getCall(0).args[0], '/source.json');
+        t.equal(transformSpy.getCall(0).args[1], 'Source');
         t.end();
     });
 
@@ -114,6 +115,7 @@ test('RasterTileSource', (t) => {
                 source.loadTile(tile, () => {});
                 t.ok(transformSpy.calledOnce);
                 t.equal(transformSpy.getCall(0).args[0], 'http://example.com/10/5/5.png');
+                t.equal(transformSpy.getCall(0).args[1], 'Tile');
                 t.end();
             }
         });
diff --git a/test/unit/source/vector_tile_source.test.js b/test/unit/source/vector_tile_source.test.js
index 3f47e23e4f3..9aa21db6ef2 100644
--- a/test/unit/source/vector_tile_source.test.js
+++ b/test/unit/source/vector_tile_source.test.js
@@ -77,7 +77,8 @@ test('VectorTileSource', (t) => {
 
         createSource({ url: "/source.json" }, transformSpy);
         window.server.respond();
-        t.ok(transformSpy.calledWith('/source.json'));
+        t.equal(transformSpy.getCall(0).args[0], '/source.json');
+        t.equal(transformSpy.getCall(0).args[1], 'Source');
         t.end();
     });
 
@@ -176,6 +177,7 @@ test('VectorTileSource', (t) => {
                 source.loadTile(tile, () => {});
                 t.ok(transformSpy.calledOnce);
                 t.equal(transformSpy.getCall(0).args[0], 'http://example.com/10/5/5.png');
+                t.equal(transformSpy.getCall(0).args[1], 'Tile');
                 t.end();
             }
         });
diff --git a/test/unit/style/style.test.js b/test/unit/style/style.test.js
index f145a533646..e4ed8799d8c 100644
--- a/test/unit/style/style.test.js
+++ b/test/unit/style/style.test.js
@@ -126,6 +126,7 @@ test('Style', (t) => {
         // window.server.respond();
         t.ok(transformSpy.calledOnce);
         t.equal(transformSpy.getCall(0).args[0], '/style.json');
+        t.equal(transformSpy.getCall(0).args[1], 'Style');
         t.end();
     });
 
@@ -154,7 +155,9 @@ test('Style', (t) => {
         style.on('style.load', () => {
             t.equal(transformSpy.callCount, 2);
             t.equal(transformSpy.getCall(0).args[0], 'http://example.com/sprites/bright-v8.json');
+            t.equal(transformSpy.getCall(0).args[1], 'SpriteJSON');
             t.equal(transformSpy.getCall(1).args[0], 'http://example.com/sprites/bright-v8.png');
+            t.equal(transformSpy.getCall(1).args[1], 'SpriteImage');
             t.end();
         });
 
diff --git a/test/unit/symbol/glyph_source.test.js b/test/unit/symbol/glyph_source.test.js
index 364ef2e4b51..f61599ad4f6 100644
--- a/test/unit/symbol/glyph_source.test.js
+++ b/test/unit/symbol/glyph_source.test.js
@@ -1,6 +1,7 @@
 'use strict';
 
 const test = require('mapbox-gl-js-test').test;
+const ajax = require('../../../src/util/ajax');
 const GlyphSource = require('../../../src/symbol/glyph_source');
 const fs = require('fs');
 
@@ -35,10 +36,11 @@ test('GlyphSource', (t) => {
     });
 
     t.test('transforms glyph URL before request', (t) => {
+        t.stub(ajax, 'getArrayBuffer').callsFake((url, cb) => cb());
         const transformSpy = t.stub().callsFake((url) => { return { url: url }; });
-        const source = new GlyphSource("https://localhost/fonts/v1/{fontstack}/{range}.pbf", false, transformSpy);
+        const source = new GlyphSource("https://localhost/fonts/v1/{fontstack}/{range}.pbf", false, null, transformSpy);
 
-        source.getSimpleGlyphs("Arial Unicode MS", [55], 0, () => {
+        source.loadPBF("https://localhost/fonts/v1/Arial Unicode MS/0-255.pbf", () => {
             t.ok(transformSpy.calledOnce);
             t.equal(transformSpy.getCall(0).args[0], "https://localhost/fonts/v1/Arial Unicode MS/0-255.pbf");
             t.end();