diff --git a/lib/generate.js b/lib/generate.js
index 3d9a34f5..ddb87adc 100644
--- a/lib/generate.js
+++ b/lib/generate.js
@@ -110,7 +110,7 @@ const getReportGroup = (reports, lcov, dataType) => {
     }
 
     // group v8 and istanbul
-    const reportGroup = {};
+    const groupMap = new Map();
     Object.keys(reportMap).forEach((k) => {
         const options = reportMap[k];
 
@@ -120,24 +120,24 @@ const getReportGroup = (reports, lcov, dataType) => {
             type = options.type || 'v8';
         }
 
-        let group = reportGroup[type];
+        let group = groupMap.get(type);
         if (!group) {
-            group = {};
-            reportGroup[type] = group;
+            group = new Map();
+            groupMap.set(type, group);
         }
 
-        group[k] = options;
+        group.set(k, options);
 
     });
 
     // requires a default istanbul report if data is istanbul
-    if (dataType === 'istanbul' && !reportGroup.istanbul) {
-        reportGroup.istanbul = {
-            html: {}
-        };
+    if (dataType === 'istanbul' && !groupMap.has('istanbul')) {
+        const istanbulGroup = new Map();
+        istanbulGroup.set('html', {});
+        groupMap.set('istanbul', istanbulGroup);
     }
 
-    return reportGroup;
+    return groupMap;
 };
 
 // ========================================================================================================
@@ -146,7 +146,7 @@ const getReportGroup = (reports, lcov, dataType) => {
 const generateV8ListReports = async (v8list, coverageData, fileSources, options) => {
     let istanbulReportPath;
     // v8 to istanbul reports
-    if (options.reportGroup.istanbul) {
+    if (options.reportGroup.has('istanbul')) {
         const istanbulCoverageResults = await saveIstanbulReports(coverageData, fileSources, options);
         istanbulReportPath = istanbulCoverageResults.reportPath;
     }
@@ -200,11 +200,9 @@ const generateCoverageReports = async (dataList, sourceCache, options) => {
     // [ 'type', 'reportPath', 'name', 'watermarks', 'summary', 'files' ]
     // console.log(Object.keys(coverageResults));
 
-    const bothGroup = options.reportGroup.both;
-    if (bothGroup) {
-        const bothReports = Object.keys(bothGroup);
-        for (const reportName of bothReports) {
-            const reportOptions = bothGroup[reportName];
+    if (options.reportGroup.has('both')) {
+        const bothGroup = options.reportGroup.get('both');
+        for (const [reportName, reportOptions] of bothGroup) {
             const builtInHandler = bothBuiltInReports[reportName];
             const t1 = Date.now();
             if (builtInHandler) {
diff --git a/lib/istanbul/istanbul.js b/lib/istanbul/istanbul.js
index 53a04a7e..10214de9 100644
--- a/lib/istanbul/istanbul.js
+++ b/lib/istanbul/istanbul.js
@@ -87,14 +87,16 @@ const saveIstanbulReports = (coverageData, fileSources, options) => {
     // create a context for report generation
     const context = istanbulLibReport.createContext(contextOptions);
 
-    const istanbulGroup = options.reportGroup.istanbul;
-    Object.keys(istanbulGroup).forEach((reportName) => {
-        const t1 = Date.now();
-        const reportOptions = istanbulGroup[reportName];
-        const report = istanbulReports.create(reportName, reportOptions);
-        report.execute(context);
-        Util.logTime(`┌ [generate] saved report: ${reportName}`, t1);
-    });
+    const istanbulGroup = options.reportGroup.get('istanbul');
+    // already has
+    if (istanbulGroup) {
+        for (const [reportName, reportOptions] of istanbulGroup) {
+            const t1 = Date.now();
+            const report = istanbulReports.create(reportName, reportOptions);
+            report.execute(context);
+            Util.logTime(`┌ [generate] saved report: ${reportName}`, t1);
+        }
+    }
 
     // add watermarks and color
     const coverageReport = new IstanbulSummary();
diff --git a/lib/v8/v8.js b/lib/v8/v8.js
index 9a76f16a..a12671fa 100644
--- a/lib/v8/v8.js
+++ b/lib/v8/v8.js
@@ -405,12 +405,10 @@ const saveV8Report = async (v8list, options, istanbulReportPath) => {
     };
 
     const outputs = {};
-    const v8Group = options.reportGroup.v8;
+    const v8Group = options.reportGroup.get('v8');
     // could be no v8 only reports, but have `both` data reports
     if (v8Group) {
-        const v8Reports = Object.keys(v8Group);
-        for (const reportName of v8Reports) {
-            const reportOptions = v8Group[reportName];
+        for (const [reportName, reportOptions] of v8Group) {
             const buildInHandler = buildInV8Reports[reportName];
             const t1 = Date.now();
             if (buildInHandler) {