diff --git a/src/babel/transformation/helpers/get-function-arity.js b/src/babel/transformation/helpers/get-function-arity.js
new file mode 100644
index 0000000000..faebae2cc7
--- /dev/null
+++ b/src/babel/transformation/helpers/get-function-arity.js
@@ -0,0 +1,9 @@
+var t = require("../../types");
+
+module.exports = function (node) {
+  var lastNonDefault = 0;
+  for (var i = 0; i < node.params.length; i++) {
+    if (!t.isAssignmentPattern(node.params[i])) lastNonDefault = i + 1;
+  }
+  return lastNonDefault;
+};
diff --git a/src/babel/transformation/helpers/name-method.js b/src/babel/transformation/helpers/name-method.js
index 31ddb8ab73..4593254130 100644
--- a/src/babel/transformation/helpers/name-method.js
+++ b/src/babel/transformation/helpers/name-method.js
@@ -1,5 +1,6 @@
-var util = require("../../util");
-var t    = require("../../types");
+var getFunctionArity = require("./get-function-arity");
+var util             = require("../../util");
+var t                = require("../../types");
 
 var visitor = {
   enter(node, parent, scope, state) {
@@ -21,12 +22,21 @@ var wrap = function (state, method, id, scope) {
   if (state.selfReference) {
     var templateName = "property-method-assignment-wrapper";
     if (method.generator) templateName += "-generator";
-    return util.template(templateName, {
+    var template = util.template(templateName, {
       FUNCTION: method,
       FUNCTION_ID: id,
       FUNCTION_KEY: scope.generateUidIdentifier(id.name),
       WRAPPER_KEY: scope.generateUidIdentifier(id.name + "Wrapper")
     });
+
+    // shim in dummy params to retain function arity, if you try to read the
+    // source then you'll get the original since it's proxied so it's all good
+    var params = template.callee.body.body[0].declarations[0].init.params;
+    for (var i = 0, len = getFunctionArity(method); i < len; i++) {
+      params.push(scope.generateUidIdentifier("x"));
+    }
+
+    return template;
   } else {
     method.id = id;
     return method;