diff --git a/index.js b/index.js
index fe9dd87..dfdae89 100644
--- a/index.js
+++ b/index.js
@@ -20,25 +20,26 @@ import ptBr from "./src/locale/pt-BR.js";
 import ruRu from "./src/locale/ru-RU.js";
 import zhCn from "./src/locale/zh-CN.js";
 
-var localeDefinitions = (new Map)
-    .set("ca-ES", caEs)
-    .set("de-DE", deDe)
-    .set("en-CA", enCa)
-    .set("en-GB", enGb)
-    .set("en-US", enUs)
-    .set("es-ES", esEs)
-    .set("fi-FI", fiFi)
-    .set("fr-CA", frCa)
-    .set("fr-FR", frFr)
-    .set("he-IL", heIl)
-    .set("it-IT", itIt)
-    .set("ja-JP", jaJp)
-    .set("mk-MK", mkMk)
-    .set("nl-NL", nlNl)
-    .set("pl-PL", plPl)
-    .set("pt-BR", ptBr)
-    .set("ru-RU", ruRu)
-    .set("zh-CN", zhCn);
+var localeDefinitions = {
+  "ca-ES": caEs,
+  "de-DE": deDe,
+  "en-CA": enCa,
+  "en-GB": enGb,
+  "en-US": enUs,
+  "es-ES": esEs,
+  "fi-FI": fiFi,
+  "fr-CA": frCa,
+  "fr-FR": frFr,
+  "he-IL": heIl,
+  "it-IT": itIt,
+  "ja-JP": jaJp,
+  "mk-MK": mkMk,
+  "nl-NL": nlNl,
+  "pl-PL": plPl,
+  "pt-BR": ptBr,
+  "ru-RU": ruRu,
+  "zh-CN": zhCn
+};
 
 var defaultLocale = locale(enUs);
 export var format = defaultLocale.format;
@@ -46,8 +47,8 @@ export var utcFormat = defaultLocale.utcFormat;
 
 export function localeFormat(definition) {
   if (typeof definition === "string") {
-    definition = localeDefinitions.get(definition);
-    if (!definition) return null;
+    if (!localeDefinitions.hasOwnProperty(definition)) return null;
+    definition = localeDefinitions[definition];
   }
   return locale(definition);
 };
diff --git a/package.json b/package.json
index bc82e0e..d1060a7 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "d3-time-format",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "description": "A JavaScript time formatter and parser inspired by strftime and strptime.",
   "keywords": [
     "d3",
@@ -22,7 +22,7 @@
     "url": "https://github.com/d3/d3-time-format.git"
   },
   "scripts": {
-    "pretest": "mkdir -p build && d3-bundler --polyfill-map --format=umd --name=timeFormat -- index.js > build/timeFormat.js",
+    "pretest": "mkdir -p build && d3-bundler --format=umd --name=timeFormat -- index.js > build/timeFormat.js",
     "test": "TZ=America/Los_Angeles faucet `find test -name '*-test.js'`",
     "prepublish": "npm run test && uglifyjs build/timeFormat.js -c -m -o build/timeFormat.min.js && rm -f build/timeFormat.zip && zip -j build/timeFormat.zip -- LICENSE README.md build/timeFormat.js build/timeFormat.min.js"
   },
diff --git a/src/locale.js b/src/locale.js
index 8dc24ea..93acd2d 100644
--- a/src/locale.js
+++ b/src/locale.js
@@ -214,22 +214,22 @@ export default function(locale) {
 
   function parseShortWeekday(d, string, i) {
     var n = shortWeekdayRe.exec(string.slice(i));
-    return n ? (d.w = shortWeekdayLookup.get(n[0].toLowerCase()), i + n[0].length) : -1;
+    return n ? (d.w = shortWeekdayLookup[n[0].toLowerCase()], i + n[0].length) : -1;
   }
 
   function parseWeekday(d, string, i) {
     var n = weekdayRe.exec(string.slice(i));
-    return n ? (d.w = weekdayLookup.get(n[0].toLowerCase()), i + n[0].length) : -1;
+    return n ? (d.w = weekdayLookup[n[0].toLowerCase()], i + n[0].length) : -1;
   }
 
   function parseShortMonth(d, string, i) {
     var n = shortMonthRe.exec(string.slice(i));
-    return n ? (d.m = shortMonthLookup.get(n[0].toLowerCase()), i + n[0].length) : -1;
+    return n ? (d.m = shortMonthLookup[n[0].toLowerCase()], i + n[0].length) : -1;
   }
 
   function parseMonth(d, string, i) {
     var n = monthRe.exec(string.slice(i));
-    return n ? (d.m = monthLookup.get(n[0].toLowerCase()), i + n[0].length) : -1;
+    return n ? (d.m = monthLookup[n[0].toLowerCase()], i + n[0].length) : -1;
   }
 
   function parseLocaleDateTime(d, string, i) {
@@ -245,7 +245,7 @@ export default function(locale) {
   }
 
   function parsePeriod(d, string, i) {
-    var n = periodLookup.get(string.slice(i, i += 2).toLowerCase());
+    var n = periodLookup[string.slice(i, i += 2).toLowerCase()];
     return n == null ? -1 : (d.p = n, i);
   }
 
@@ -326,8 +326,8 @@ function formatRe(names) {
 }
 
 function formatLookup(names) {
-  var map = new Map, i = -1, n = names.length;
-  while (++i < n) map.set(names[i].toLowerCase(), i);
+  var map = {}, i = -1, n = names.length;
+  while (++i < n) map[names[i].toLowerCase()] = i;
   return map;
 }