diff --git a/src/core/obj.js b/src/core/obj.js
index 60465c864..4de709ced 100644
--- a/src/core/obj.js
+++ b/src/core/obj.js
@@ -1046,8 +1046,8 @@ var XRef = (function XRefClosure() {
     // prepare the XRef cache
     this.cache = [];
     this.stats = {
-      streamTypes: [],
-      fontTypes: [],
+      streamTypes: Object.create(null),
+      fontTypes: Object.create(null),
     };
   }
 
diff --git a/src/display/api.js b/src/display/api.js
index bea055001..263a534c6 100644
--- a/src/display/api.js
+++ b/src/display/api.js
@@ -205,10 +205,10 @@ function setPDFNetworkStreamFactory(pdfNetworkStreamFactory) {
 
 /**
  * @typedef {Object} PDFDocumentStats
- * @property {Array} streamTypes - Used stream types in the document (an item
+ * @property {Object} streamTypes - Used stream types in the document (an item
  *   is set to true if specific stream ID was used in the document).
- * @property {Array} fontTypes - Used font type in the document (an item is set
- *   to true if specific font ID was used in the document).
+ * @property {Object} fontTypes - Used font types in the document (an item
+ *   is set to true if specific font ID was used in the document).
  */
 
 /**
diff --git a/test/unit/api_spec.js b/test/unit/api_spec.js
index cac5fec01..26a0a8f7d 100644
--- a/test/unit/api_spec.js
+++ b/test/unit/api_spec.js
@@ -926,7 +926,7 @@ describe('api', function() {
     it('gets document stats', function(done) {
       var promise = doc.getStats();
       promise.then(function (stats) {
-        expect(stats).toEqual({ streamTypes: [], fontTypes: [], });
+        expect(stats).toEqual({ streamTypes: {}, fontTypes: {}, });
         done();
       }).catch(done.fail);
     });
@@ -1293,9 +1293,9 @@ describe('api', function() {
       var promise = page.getOperatorList().then(function () {
         return pdfDocument.getStats();
       });
-      var expectedStreamTypes = [];
+      var expectedStreamTypes = {};
       expectedStreamTypes[StreamType.FLATE] = true;
-      var expectedFontTypes = [];
+      var expectedFontTypes = {};
       expectedFontTypes[FontType.TYPE1] = true;
       expectedFontTypes[FontType.CIDFONTTYPE2] = true;