diff --git a/packages/code/src/function.js b/packages/code/src/function.js
index 7ce6881..2606337 100644
--- a/packages/code/src/function.js
+++ b/packages/code/src/function.js
@@ -72,6 +72,13 @@ function flattenParams(ast) {
 
 export function hasExternalDependency(ast) {
   const locals = flattenParams(ast);
+  locals.push(
+    'global',
+    'super',
+    'window',
+    'Math',
+    // ... @todo
+  );
   const idWalker = walk({
     Identifier: ({name}) => {
       locals.push(name);
diff --git a/packages/code/test/function.js b/packages/code/test/function.js
index a4491ce..630dc46 100644
--- a/packages/code/test/function.js
+++ b/packages/code/test/function.js
@@ -43,11 +43,31 @@ it('can identify external dependencies', () => {
   ))
     .to.be.true;
 
+  expect(hasExternalDependency(
+    extractFunction(parse('function test(a, b) { c.a.b; }')),
+  ))
+    .to.be.true;
+
+  expect(hasExternalDependency(
+    extractFunction(parse('function test(a, b) { c.d; }')),
+  ))
+    .to.be.true;
+
+  expect(hasExternalDependency(
+    extractFunction(parse('function test(a, b) { Math.min(a, b); }')),
+  ))
+    .to.be.false;
+
   expect(hasExternalDependency(
     extractFunction(parse('function test(a, b) { this.whatever; }')),
   ))
     .to.be.false;
 
+  expect(hasExternalDependency(
+    extractFunction(parse('function test(a, b) { this.foo.whatever }')),
+  ))
+    .to.be.false;
+
   expect(hasExternalDependency(
     extractFunction(parse('function test(a, b) { console.log("HI"); }')),
   ))