diff --git a/src/report/report-builders.js b/src/report/report-builders.js
index 956363c8..57b99449 100644
--- a/src/report/report-builders.js
+++ b/src/report/report-builders.js
@@ -29,7 +29,7 @@ function calculateResult(assertions) {
 // add an assertion and recalc the top-level result
 function withAssertions(obj, assertions) {
   if (!('assertions' in obj)) obj.assertions = [];
-  obj.assertions.push(assertions);
+  obj.assertions = obj.assertions.concat(assertions);
   obj['earl:result'] = calculateResult(obj.assertions);
   return obj;
 }
@@ -90,8 +90,8 @@ class ReportBuilder {
     this._json = {
       '@type': 'earl:report',
       '@context': 'http://ace.daisy.org/ns/ace-report._jsonld',
-      'dct:title': title,
-      'dct:description': description,
+      'dct:title': (title == null) ? '' : title.toString(),
+      'dct:description': (title == null) ? '' : description.toString(),
       'dct:date': new Date().toLocaleString(),
       'earl:assertedBy': ACE_DESCRIPTION,
       outlines: {},
@@ -103,37 +103,47 @@ class ReportBuilder {
     return this._json;
   }
   withA11yMeta(metadata) {
+    if (!metadata) return this;
     this._json['a11y-metadata'] = metadata;
     return this;
   }
   withAssertions(assertions) {
+    if (!assertions) return this;
     withAssertions(this._json, assertions);
     return this;
   }
   withData(data) {
+    if (!data) return this;
     Object.getOwnPropertyNames(data).forEach((key) => {
-      this._json.data[key] = (Array.isArray(this._json.data[key]))
-        ? this._json.data[key].push(data[key])
-        : data[key];
+      if (Array.isArray(this._json.data[key])) {
+        this._json.data[key] = this._json.data[key].concat(data[key]);
+      } else {
+        this._json.data[key] = data[key];
+      }
     });
+    return this;
   }
   withEPUBOutline(outline) {
+    if (!outline) return this;
     this._json.outlines.toc = outline;
     return this;
   }
   withHeadingsOutline(outline) {
+    if (!outline) return this;
     this._json.outlines.headings = outline;
     return this;
   }
   withHTMLOutline(outline) {
+    if (!outline) return this;
     this._json.outlines.html = outline;
     return this;
   }
   withProperties(properties) {
+    if (!properties) return this;
     Object.getOwnPropertyNames(properties).forEach((key) => {
-      this._json.properties[key] = (key in properties)
-        ? this._json.properties[key] || properties[key]
-        : properties[key];
+      this._json.properties[key] = (key in this._json.properties)
+        ? this._json.properties[key] || Boolean(properties[key])
+        : Boolean(properties[key]);
     });
     return this;
   }
diff --git a/src/report/report-builders.test.js b/src/report/report-builders.test.js
new file mode 100644
index 00000000..66789712
--- /dev/null
+++ b/src/report/report-builders.test.js
@@ -0,0 +1,192 @@
+'use strict';
+
+const builders = require('./report-builders');
+const pkg = require('../../package');
+
+describe('report builder', () => {
+  let report;
+
+  beforeEach(() => {
+    report = new builders.ReportBuilder();
+  });
+
+  describe('creating a new report', () => {
+    test('new report is well formed', () => {
+      expect(report).toBeDefined();
+      expect(report.build()).toBeDefined();
+      expect(report.build()).toMatchObject({
+        '@type': 'earl:report',
+        '@context': 'http://ace.daisy.org/ns/ace-report.jsonld',
+        'dct:title': 'Ace Report',
+        'dct:description': 'Report on automated accessibility checks for EPUB',
+        'earl:assertedBy': {
+          '@type': 'earl:software',
+          'doap:name': 'DAISY Ace',
+          'doap:description': 'DAISY Accessibility Checker for EPUB',
+          'doap:homepage': 'http://ace.daisy.org',
+          'doap:created': '2017-07-01',
+          'doap:release': { 'doap:revision': pkg.version },
+        },
+      });
+      expect(report.build().data).toBeDefined();
+      expect(report.build().outlines).toBeDefined();
+      expect(report.build().properties).toBeDefined();
+      expect(report.build().assertions).toBeUndefined();
+    });
+    test('new report args are used', () => {
+      report = new builders.ReportBuilder('Title', 'Desc');
+      expect(report).toBeDefined();
+      expect(report.build()).toBeDefined();
+      expect(report.build()).toMatchObject({
+        'dct:title': 'Title',
+        'dct:description': 'Desc',
+      });
+    });
+    test('new report undefined args are ignored', () => {
+      report = new builders.ReportBuilder(undefined, undefined);
+      expect(report).toBeDefined();
+      expect(report.build()).toBeDefined();
+      expect(report.build()).toMatchObject({
+        'dct:title': 'Ace Report',
+        'dct:description': 'Report on automated accessibility checks for EPUB',
+      });
+    });
+    test('new report null args contains empty string values', () => {
+      report = new builders.ReportBuilder(null, null);
+      expect(report).toBeDefined();
+      expect(report.build()).toBeDefined();
+      expect(report.build()).toMatchObject({
+        'dct:title': '',
+        'dct:description': '',
+      });
+    });
+    test('new report with object args contains toString values', () => {
+      report = new builders.ReportBuilder({}, {});
+      expect(report).toBeDefined();
+      expect(report.build()).toBeDefined();
+      expect(report.build()).toMatchObject({
+        'dct:title': '[object Object]',
+        'dct:description': '[object Object]',
+      });
+    });
+  });
+  describe('adding assertions', () => {
+    let assertions;
+    test('adding null assertion is ignored', () => {
+      expect(report.withAssertions(null)).toBeDefined();
+      expect(report.build().assertions).toBeUndefined();
+    });
+    test('adding undefined assertion is ignored', () => {
+      expect(report.withAssertions(undefined)).toBeDefined();
+      expect(report.build().assertions).toBeUndefined();
+    });
+    test('adding single assertion to empty report creates a new array', () => {
+      expect(report.withAssertions({ foo: 'foo' })).toBeDefined();
+      assertions = report.build().assertions;
+      expect(assertions).toBeDefined();
+      expect(Array.isArray(assertions)).toBe(true);
+      expect(assertions.length).toBe(1);
+      expect(assertions[0]).toEqual({ foo: 'foo' });
+    });
+    test('adding single assertion adds to existing assertions', () => {
+      expect(report.withAssertions({ foo: 'foo' })).toBeDefined();
+      assertions = report.build().assertions;
+      expect(assertions).toBeDefined();
+      expect(Array.isArray(assertions)).toBe(true);
+      expect(assertions.length).toBe(1);
+      expect(assertions[0]).toEqual({ foo: 'foo' });
+    });
+    test('adding assertions array to empty report copies it to the report', () => {
+      expect(report.withAssertions([
+        { foo: 'foo' }, { foo: 'foo' },
+      ])).toBeDefined();
+      assertions = report.build().assertions;
+      expect(assertions).toBeDefined();
+      expect(Array.isArray(assertions)).toBe(true);
+      expect(assertions.length).toBe(2);
+      expect(assertions[0]).toEqual({ foo: 'foo' });
+    });
+    test('adding assertions array concatenates to existing array', () => {
+      expect(report.withAssertions({ bar: 'bar' })).toBeDefined();
+      expect(report.withAssertions([
+        { foo: 'foo' }, { foo: 'foo' },
+      ])).toBeDefined();
+      assertions = report.build().assertions;
+      expect(assertions).toBeDefined();
+      expect(Array.isArray(assertions)).toBe(true);
+      expect(assertions.length).toBe(3);
+      expect(assertions[0]).toEqual({ bar: 'bar' });
+      expect(assertions[1]).toEqual({ foo: 'foo' });
+    });
+  });
+  describe('adding data', () => {
+    let data;
+    beforeEach(() => {
+      data = report.build().data;
+    });
+    test('adding null data` is ignored', () => {
+      expect(report.withData(null)).toBeDefined();
+      expect(data).toEqual({});
+    });
+    test('adding undefined data is ignored', () => {
+      expect(report.withData(undefined)).toBeDefined();
+      expect(data).toEqual({});
+    });
+    test('adding data to new report populates the data section', () => {
+      expect(report.withData({ foo: 'foo' })).toBeDefined();
+      expect(data).toEqual({ foo: 'foo' });
+    });
+    test('adding data is merged in existing data', () => {
+      expect(report.withData({ foo: 'foo' })).toBeDefined();
+      expect(report.withData({ bar: 'bar' })).toBeDefined();
+      expect(data).toEqual({ foo: 'foo', bar: 'bar' });
+    });
+    test('adding data overrides existing scalar data', () => {
+      expect(report.withData({ foo: 'foo' })).toBeDefined();
+      expect(report.withData({ foo: 'bar' })).toBeDefined();
+      expect(data).toEqual({ foo: 'bar' });
+    });
+    test('adding data adds to existing array data', () => {
+      expect(report.withData({ foo: ['foo'] })).toBeDefined();
+      expect(report.withData({ foo: ['bar'] })).toBeDefined();
+      expect(data).toEqual({ foo: ['foo', 'bar'] });
+    });
+  });
+  describe('adding properties', () => {
+    let properties;
+    beforeEach(() => {
+      properties = report.build().properties;
+    });
+    test('adding null properties` is ignored', () => {
+      expect(report.withProperties(null)).toBeDefined();
+      expect(properties).toEqual({});
+    });
+    test('adding undefined properties is ignored', () => {
+      expect(report.withProperties(undefined)).toBeDefined();
+      expect(properties).toEqual({});
+    });
+    test('adding properties to new report populates the properties section', () => {
+      expect(report.withProperties({ foo: true })).toBeDefined();
+      expect(properties).toEqual({ foo: true });
+    });
+    test('adding properties augments existing properties', () => {
+      expect(report.withProperties({ foo: true })).toBeDefined();
+      expect(report.withProperties({ bar: true })).toBeDefined();
+      expect(properties).toEqual({ foo: true, bar: true });
+    });
+    test('adding properties keeps existing true properties', () => {
+      expect(report.withProperties({ foo: true })).toBeDefined();
+      expect(report.withProperties({ foo: false })).toBeDefined();
+      expect(properties).toEqual({ foo: true });
+    });
+    test('adding properties booleanizes values', () => {
+      expect(report.withProperties({ foo: 'hello', bar: null })).toBeDefined();
+      expect(properties).toEqual({ foo: true, bar: false });
+    });
+    test('adding properties booleanizes values when overrinding too', () => {
+      expect(report.withProperties({ foo: false })).toBeDefined();
+      expect(report.withProperties({ foo: [] })).toBeDefined();
+      expect(properties).toEqual({ foo: true });
+    });
+  });
+});
diff --git a/tests/__tests__/parsing.test.js b/tests/__tests__/parsing.test.js
index 04482139..e7b073fe 100644
--- a/tests/__tests__/parsing.test.js
+++ b/tests/__tests__/parsing.test.js
@@ -40,3 +40,8 @@ test('issue #49: multiple \'dc:title\' elements', async () => {
   const report = await ace('../data/issue49');
   expect(report['earl:result']['earl:outcome']).toEqual('pass');
 });
+
+test.only('issue #53: XXX', async () => {
+  const report = await ace('../data/issue53');
+  expect(report['earl:result']['earl:outcome']).toEqual('pass');
+});
diff --git a/tests/data/issue53/EPUB/content_001.xhtml b/tests/data/issue53/EPUB/content_001.xhtml
new file mode 100644
index 00000000..d0e7d2ff
--- /dev/null
+++ b/tests/data/issue53/EPUB/content_001.xhtml
@@ -0,0 +1,10 @@
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en">
+<head>
+<title>Minimal EPUB</title>
+</head>
+<body>
+<h1>Loomings</h1>
+<p>Call me Ishmael.</p>
+<img src="image_001.jpg" alt="dummy"/>
+</body>
+</html>
diff --git a/tests/data/issue53/EPUB/content_002.xhtml b/tests/data/issue53/EPUB/content_002.xhtml
new file mode 100644
index 00000000..d0e7d2ff
--- /dev/null
+++ b/tests/data/issue53/EPUB/content_002.xhtml
@@ -0,0 +1,10 @@
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en">
+<head>
+<title>Minimal EPUB</title>
+</head>
+<body>
+<h1>Loomings</h1>
+<p>Call me Ishmael.</p>
+<img src="image_001.jpg" alt="dummy"/>
+</body>
+</html>
diff --git a/tests/data/issue53/EPUB/image_001.jpg b/tests/data/issue53/EPUB/image_001.jpg
new file mode 100644
index 00000000..d2c2e1ac
--- /dev/null
+++ b/tests/data/issue53/EPUB/image_001.jpg
@@ -0,0 +1 @@
+fake image
diff --git a/tests/data/issue53/EPUB/nav.xhtml b/tests/data/issue53/EPUB/nav.xhtml
new file mode 100644
index 00000000..1d538c19
--- /dev/null
+++ b/tests/data/issue53/EPUB/nav.xhtml
@@ -0,0 +1,12 @@
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en">
+<head>
+<title>Minimal Nav</title>
+</head>
+<body>
+<nav epub:type="toc">
+<ol>
+<li><a href="content_001.xhtml">content 001</a></li>
+</ol>
+</nav>
+</body>
+</html>
diff --git a/tests/data/issue53/EPUB/package.opf b/tests/data/issue53/EPUB/package.opf
new file mode 100644
index 00000000..b94bf0e6
--- /dev/null
+++ b/tests/data/issue53/EPUB/package.opf
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" xml:lang="en" unique-identifier="uid">
+<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
+  <dc:title id="title">Minimal EPUB 3.0</dc:title>
+  <dc:language>en</dc:language>
+  <dc:identifier id="uid">NOID</dc:identifier>
+  <meta property="dcterms:modified">2017-01-01T00:00:01Z</meta>
+  <meta property="dcterms:modified">2017-01-01T00:00:01Z</meta>
+  <meta property="schema:accessibilityFeature">structuralNavigation</meta>
+  <meta property="schema:accessibilitySummary">everything OK!</meta>
+  <meta property="schema:accessibilityHazard">noFlashingHazard</meta>
+  <meta property="schema:accessibilityHazard">noSoundHazard</meta>
+  <meta property="schema:accessibilityHazard">noMotionSimulationHazard</meta>
+  <meta property="schema:accessMode">textual</meta>
+  <meta property="schema:accessModeSufficient">textual</meta>
+</metadata>
+<manifest>
+  <item id="nav"  href="nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
+  <item id="content_001"  href="content_001.xhtml" media-type="application/xhtml+xml"/>
+  <item id="content_002"  href="content_002.xhtml" media-type="application/xhtml+xml"/>
+  <item id="image_001"  href="image_001.jpg" media-type="image/jpeg"/>
+</manifest>
+<spine>
+  <itemref idref="content_001" />
+  <itemref idref="content_002" />
+</spine>
+</package>
diff --git a/tests/data/issue53/META-INF/container.xml b/tests/data/issue53/META-INF/container.xml
new file mode 100644
index 00000000..2cf00654
--- /dev/null
+++ b/tests/data/issue53/META-INF/container.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
+   <rootfiles>
+      <rootfile full-path="EPUB/package.opf" media-type="application/oebps-package+xml"/>
+   </rootfiles>
+</container>
diff --git a/tests/data/issue53/mimetype b/tests/data/issue53/mimetype
new file mode 100644
index 00000000..57ef03f2
--- /dev/null
+++ b/tests/data/issue53/mimetype
@@ -0,0 +1 @@
+application/epub+zip
\ No newline at end of file