diff --git a/packages/istanbul-api/lib/file-matcher.js b/packages/istanbul-api/lib/file-matcher.js
index c41d98ad..c9c6b330 100644
--- a/packages/istanbul-api/lib/file-matcher.js
+++ b/packages/istanbul-api/lib/file-matcher.js
@@ -58,7 +58,7 @@ function matcherFor(options, callback) {
     options.realpath = true; //force real paths (to match Node.js module paths)
 
     filesFor(options, function (err, files) {
-        var fileMap = {},
+        var fileMap = Object.create(null),
             matchFn;
         /* istanbul ignore if - untestable */
         if (err) { return callback(err); }
diff --git a/packages/istanbul-lib-coverage/lib/coverage-map.js b/packages/istanbul-lib-coverage/lib/coverage-map.js
index ccb3c8a4..27ef6193 100644
--- a/packages/istanbul-lib-coverage/lib/coverage-map.js
+++ b/packages/istanbul-lib-coverage/lib/coverage-map.js
@@ -8,7 +8,7 @@ var FileCoverage = require('./file').FileCoverage,
     CoverageSummary = require('./file').CoverageSummary;
 
 function loadMap(source) {
-    var data = {};
+    var data = Object.create(null);
     Object.keys(source).forEach(function (k) {
         var cov = source[k];
         if (cov instanceof FileCoverage) {
@@ -27,7 +27,7 @@ function loadMap(source) {
  */
 function CoverageMap(obj) {
     if (!obj) {
-        this.data = {};
+        this.data = Object.create(null);
     } else if (obj instanceof CoverageMap) {
         this.data = obj.data;
     } else {
diff --git a/packages/istanbul-lib-coverage/lib/file.js b/packages/istanbul-lib-coverage/lib/file.js
index a85562f1..570b274e 100644
--- a/packages/istanbul-lib-coverage/lib/file.js
+++ b/packages/istanbul-lib-coverage/lib/file.js
@@ -170,7 +170,7 @@ function FileCoverage(pathOrObj) {
 FileCoverage.prototype.getLineCoverage = function () {
     var statementMap = this.data.statementMap,
         statements = this.data.s,
-        lineMap = {};
+        lineMap = Object.create(null);
 
     Object.keys(statements).forEach(function (st) {
         if (!statementMap[st]) {
diff --git a/packages/istanbul-lib-report/lib/summarizer.js b/packages/istanbul-lib-report/lib/summarizer.js
index ee353b31..93c431b7 100644
--- a/packages/istanbul-lib-report/lib/summarizer.js
+++ b/packages/istanbul-lib-report/lib/summarizer.js
@@ -166,7 +166,7 @@ function toInitialList(coverageMap) {
 }
 
 function toDirParents(list) {
-    var nodeMap = {},
+    var nodeMap = Object.create(null),
         parentNodeList = [];
     list.forEach(function (o) {
         var node = new ReportNode(o.path, o.fileCoverage),
diff --git a/packages/istanbul-lib-report/test/summarizer.test.js b/packages/istanbul-lib-report/test/summarizer.test.js
index cdfbf493..3db964e7 100644
--- a/packages/istanbul-lib-report/test/summarizer.test.js
+++ b/packages/istanbul-lib-report/test/summarizer.test.js
@@ -30,6 +30,19 @@ function makeCoverage(filePath, numStatements, numCovered) {
     return fc;
 }
 
+function protoDirMap(dir) {
+    var files = ['constructor.js', 'toString.js'],
+        count = 0,
+        map = {};
+    files.forEach(function (f) {
+        var filePath = dir ? dir + '/' + f : f,
+            fc = makeCoverage(filePath, 4, count);
+        count += 1;
+        map[filePath] = fc;
+    });
+    return coverage.createCoverageMap(map);
+}
+
 function singleDirMap(dir) {
     var files = ['file3.js', 'file4.js', 'file2.js', 'file1.js'],
         count = 0,
@@ -107,6 +120,13 @@ describe('summarizer', function () {
             assert.deepEqual(nodes, ['g:', 'f:file1.js', 'f:file2.js', 'f:file3.js', 'f:file4.js']);
         });
 
+        it('supports a list of files containing Object.prototype names', function () {
+            var map = protoDirMap(),
+                tree = fn(map),
+                nodes = getStructure(tree);
+            assert.deepEqual(nodes, ['g:', 'f:constructor.js', 'f:toString.js']);
+        });
+
         it('supports a list of files at the same nesting level', function () {
             var map = singleDirMap('/lib/handlers'),
                 tree = fn(map),
diff --git a/packages/istanbul-lib-source-maps/lib/map-store.js b/packages/istanbul-lib-source-maps/lib/map-store.js
index 8b31d422..f553c834 100644
--- a/packages/istanbul-lib-source-maps/lib/map-store.js
+++ b/packages/istanbul-lib-source-maps/lib/map-store.js
@@ -29,7 +29,7 @@ function MapStore(opts) {
     this.baseDir = opts.baseDir || null;
     this.verbose = opts.verbose || false;
     this.sourceStore = sourceStore.create(opts.sourceStore, { tmpdir: opts.tmpdir});
-    this.data = {};
+    this.data = Object.create(null);
 }
 /**
  * registers a source map URL with this store. It makes some input sanity checks
diff --git a/packages/istanbul-lib-source-maps/test/map-store.test.js b/packages/istanbul-lib-source-maps/test/map-store.test.js
index 200f846f..f2959455 100644
--- a/packages/istanbul-lib-source-maps/test/map-store.test.js
+++ b/packages/istanbul-lib-source-maps/test/map-store.test.js
@@ -14,6 +14,8 @@ describe('map store', function () {
     var coverageMap = libCoverage.createCoverageMap(coverageData);
 
     var transformed = mapStore.transformCoverage(coverageMap);
+    assert.isUndefined(transformed.map.data.constructor);
+    
     var transformedCoverage = transformed.map.data[path.resolve("./test.ts")].data;
 
     assert.deepEqual(transformedCoverage.statementMap, {