diff --git a/lib/6to5/transformation/helpers/define-map.js b/lib/6to5/transformation/helpers/define-map.js
new file mode 100644
index 0000000000..0019351782
--- /dev/null
+++ b/lib/6to5/transformation/helpers/define-map.js
@@ -0,0 +1,71 @@
+var clone = require("lodash/lang/clone");
+var each  = require("lodash/collection/each");
+var has   = require("lodash/object/has");
+var t     = require("../../types");
+
+exports.push = function (mutatorMap, key, kind, computed, value) {
+  var alias;
+
+  if (t.isIdentifier(key)) {
+    alias = key.name;
+    if (computed) alias = "computed:" + alias;
+  } else if (t.isLiteral(key)) {
+    alias = String(key.value);
+  } else {
+    alias = JSON.stringify(traverse.removeProperties(cloneDeep(key)));
+  }
+
+  var map;
+  if (has(mutatorMap, alias)) {
+    map = mutatorMap[alias];
+  } else {
+    map = {};
+  }
+  mutatorMap[alias] = map;
+
+  map._key = key;
+  if (computed) {
+    map._computed = true;
+  }
+
+  map[kind] = value;
+};
+
+exports.build = function (mutatorMap) {
+  var objExpr = t.objectExpression([]);
+
+  each(mutatorMap, function (map) {
+    var mapNode = t.objectExpression([]);
+
+    var propNode = t.property("init", map._key, mapNode, map._computed);
+
+    if (!map.get && !map.set) {
+      map.writable = t.literal(true);
+    }
+
+    if (map.enumerable === false) {
+      delete map.enumerable;
+    } else {
+      map.enumerable = t.literal(true);
+    }
+
+    map.configurable = t.literal(true);
+
+    each(map, function (node, key) {
+      if (key[0] === "_") return;
+
+      node = clone(node);
+      var inheritNode = node;
+      if (t.isMethodDefinition(node)) node = node.value;
+
+      var prop = t.property("init", t.identifier(key), node);
+      t.inheritsComments(prop, inheritNode);
+      t.removeComments(inheritNode);
+      mapNode.properties.push(prop);
+    });
+
+    objExpr.properties.push(propNode);
+  });
+
+  return objExpr;
+};
diff --git a/lib/6to5/transformation/transformers/es5/properties.mutators.js b/lib/6to5/transformation/transformers/es5/properties.mutators.js
index ede62a061d..515ed5fd01 100644
--- a/lib/6to5/transformation/transformers/es5/properties.mutators.js
+++ b/lib/6to5/transformation/transformers/es5/properties.mutators.js
@@ -1,7 +1,8 @@
 "use strict";
 
-var util = require("../../../util");
-var t    = require("../../../types");
+var defineMap = require("../../helpers/define-map");
+var util      = require("../../../util");
+var t         = require("../../../types");
 
 exports.ObjectExpression = function (node) {
   var mutatorMap = {};
@@ -10,7 +11,7 @@ exports.ObjectExpression = function (node) {
   node.properties = node.properties.filter(function (prop) {
     if (prop.kind === "get" || prop.kind === "set") {
       hasAny = true;
-      util.pushMutatorMap(mutatorMap, prop.key, prop.kind, prop.computed, prop.value);
+      defineMap.push(mutatorMap, prop.key, prop.kind, prop.computed, prop.value);
       return false;
     } else {
       return true;
@@ -21,6 +22,6 @@ exports.ObjectExpression = function (node) {
 
   return t.callExpression(
     t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
-    [node, util.buildDefineProperties(mutatorMap)]
+    [node, defineMap.build(mutatorMap)]
   );
 };
diff --git a/lib/6to5/transformation/transformers/es6/classes.js b/lib/6to5/transformation/transformers/es6/classes.js
index acd0af6087..1b025d72f6 100644
--- a/lib/6to5/transformation/transformers/es6/classes.js
+++ b/lib/6to5/transformation/transformers/es6/classes.js
@@ -2,6 +2,7 @@
 
 var ReplaceSupers = require("../../helpers/replace-supers");
 var nameMethod    = require("../../helpers/name-method");
+var defineMap     = require("../../helpers/define-map");
 var util          = require("../../../util");
 var t             = require("../../../types");
 
@@ -173,11 +174,11 @@ Class.prototype.buildBody = function () {
   var staticProps;
 
   if (this.hasInstanceMutators) {
-    instanceProps = util.buildDefineProperties(this.instanceMutatorMap);
+    instanceProps = defineMap.build(this.instanceMutatorMap);
   }
 
   if (this.hasStaticMutators) {
-    staticProps = util.buildDefineProperties(this.staticMutatorMap);
+    staticProps = defineMap.build(this.staticMutatorMap);
   }
 
   if (instanceProps || staticProps) {
@@ -230,8 +231,8 @@ Class.prototype.pushMethod = function (node) {
     this.hasInstanceMutators = true;
   }
 
-  util.pushMutatorMap(mutatorMap, methodName, kind, node.computed, node);
-  util.pushMutatorMap(mutatorMap, methodName, "enumerable", node.computed, false);
+  defineMap.push(mutatorMap, methodName, kind, node.computed, node);
+  defineMap.push(mutatorMap, methodName, "enumerable", node.computed, false);
 };
 
 /**
diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index bf541e1a8a..17f120f288 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -81,73 +81,6 @@ exports.sourceMapToComment = function (map) {
   return "//# sourceMappingURL=data:application/json;base64," + base64;
 };
 
-exports.pushMutatorMap = function (mutatorMap, key, kind, computed, value) {
-  var alias;
-
-  if (t.isIdentifier(key)) {
-    alias = key.name;
-    if (computed) alias = "computed:" + alias;
-  } else if (t.isLiteral(key)) {
-    alias = String(key.value);
-  } else {
-    alias = JSON.stringify(traverse.removeProperties(cloneDeep(key)));
-  }
-
-  var map;
-  if (has(mutatorMap, alias)) {
-    map = mutatorMap[alias];
-  } else {
-    map = {};
-  }
-  mutatorMap[alias] = map;
-
-  map._key = key;
-  if (computed) {
-    map._computed = true;
-  }
-
-  map[kind] = value;
-};
-
-exports.buildDefineProperties = function (mutatorMap) {
-  var objExpr = t.objectExpression([]);
-
-  each(mutatorMap, function (map) {
-    var mapNode = t.objectExpression([]);
-
-    var propNode = t.property("init", map._key, mapNode, map._computed);
-
-    if (!map.get && !map.set) {
-      map.writable = t.literal(true);
-    }
-
-    if (map.enumerable === false) {
-      delete map.enumerable;
-    } else {
-      map.enumerable = t.literal(true);
-    }
-
-    map.configurable = t.literal(true);
-
-    each(map, function (node, key) {
-      if (key[0] === "_") return;
-
-      node = clone(node);
-      var inheritNode = node;
-      if (t.isMethodDefinition(node)) node = node.value;
-
-      var prop = t.property("init", t.identifier(key), node);
-      t.inheritsComments(prop, inheritNode);
-      t.removeComments(inheritNode);
-      mapNode.properties.push(prop);
-    });
-
-    objExpr.properties.push(propNode);
-  });
-
-  return objExpr;
-};
-
 var templateVisitor = {
   enter: function (node, parent, scope, context, nodes) {
     if (t.isIdentifier(node) && has(nodes, node.name)) {