diff --git a/lib/range.js b/lib/range.js
index 7539a28..9ed9074 100644
--- a/lib/range.js
+++ b/lib/range.js
@@ -3,8 +3,8 @@
 
 exports.Range = Range;
 
-exports.extendNative = function() {
-  global.Range = Range;
+exports.extendNative = function(context) {
+  context.Range = Range;
 };
 
 function Range(start, length) {
diff --git a/lib/repr.js b/lib/repr.js
index a022e36..e852ad5 100644
--- a/lib/repr.js
+++ b/lib/repr.js
@@ -4,8 +4,8 @@
 // readable string representations of values
 exports.repr = repr;
 
-exports.extendNative = function() {
-  global.repr = repr;
+exports.extendNative = function(context) {
+  context.repr = repr;
 };
 
 function repr(x) {
diff --git a/lib/set.js b/lib/set.js
index d72159d..3ebfaa1 100644
--- a/lib/set.js
+++ b/lib/set.js
@@ -3,8 +3,8 @@
 
 exports.Set = Set;
 
-exports.extendNative = function() {
-  global.Set = Set;
+exports.extendNative = function(context) {
+  context.Set = Set;
 };
 
 var ownProps = Object.getOwnPropertyNames;