diff --git a/src/Bundle.js b/src/Bundle.js
index b0ef4ac..bdb7da8 100644
--- a/src/Bundle.js
+++ b/src/Bundle.js
@@ -1,4 +1,3 @@
-import Promise from 'es6-promise/lib/es6-promise/promise.js';
 import MagicString from 'magic-string';
 import first from './utils/first.js';
 import { blank, forOwn, keys } from './utils/object.js';
@@ -10,6 +9,7 @@ import { load, makeOnwarn, resolveId } from './utils/defaults.js';
 import getExportMode from './utils/getExportMode.js';
 import getIndentString from './utils/getIndentString.js';
 import { unixizePath } from './utils/normalizePlatform.js';
+import { mapSequence } from './utils/promise.js';
 import transform from './utils/transform.js';
 import transformBundle from './utils/transformBundle.js';
 import collapseSourcemaps from './utils/collapseSourcemaps.js';
@@ -175,7 +175,7 @@ export default class Bundle {
 	}
 
 	fetchAllDependencies ( module ) {
-		const promises = module.sources.map( source => {
+		return mapSequence( module.sources, source => {
 			return this.resolveId( source, module.id )
 				.then( resolvedId => {
 					// If the `resolvedId` is supposed to be external, make it so.
@@ -205,8 +205,6 @@ export default class Bundle {
 					}
 				});
 		});
-
-		return Promise.all( promises );
 	}
 
 	render ( options = {} ) {
diff --git a/src/Module.js b/src/Module.js
index 7764a08..4b2e7d4 100644
--- a/src/Module.js
+++ b/src/Module.js
@@ -102,37 +102,37 @@ export default class Module {
 			this.declarations.default = new SyntheticDefaultDeclaration( node, statement, identifier || this.basename() );
 		}
 
-		// export { foo, bar, baz }
 		// export var { foo, bar } = ...
 		// export var foo = 42;
 		// export var a = 1, b = 2, c = 3;
 		// export function foo () {}
-		else if ( node.type === 'ExportNamedDeclaration' ) {
+		else if ( node.declaration ) {
+			let declaration = node.declaration;
+
+			if ( declaration.type === 'VariableDeclaration' ) {
+				declaration.declarations.forEach( decl => {
+					extractNames( decl.id ).forEach( localName => {
+						this.exports[ localName ] = { localName };
+					});
+				});
+			} else {
+				// export function foo () {}
+				const localName = declaration.id.name;
+				this.exports[ localName ] = { localName };
+			}
+		}
+
+		// export { foo, bar, baz }
+		else {
 			if ( node.specifiers.length ) {
-				// export { foo, bar, baz }
 				node.specifiers.forEach( specifier => {
 					const localName = specifier.local.name;
 					const exportedName = specifier.exported.name;
 
 					this.exports[ exportedName ] = { localName };
 				});
-			}
-
-			else {
-				let declaration = node.declaration;
-
-				if ( declaration.type === 'VariableDeclaration' ) {
-					declaration.declarations.forEach( decl => {
-						extractNames( decl.id ).forEach( localName => {
-							this.exports[ localName ] = { localName };
-						});
-					});
-				}
-				else {
-					// export function foo () {}
-					const localName = declaration.id.name;
-					this.exports[ localName ] = { localName };
-				}
+			} else {
+				this.bundle.onwarn( `Module ${this.id} has an empty export declaration` );
 			}
 		}
 	}
diff --git a/src/ast/isReference.js b/src/ast/isReference.js
index 0c9a9d7..c2e6c89 100644
--- a/src/ast/isReference.js
+++ b/src/ast/isReference.js
@@ -10,7 +10,9 @@ export default function isReference ( node, parent ) {
 		if ( !parent ) return true;
 
 		// TODO is this right?
-		if ( parent.type === 'MemberExpression' ) return parent.computed || node === parent.object;
+		if ( parent.type === 'MemberExpression' || parent.type === 'MethodDefinition' ) {
+			return parent.computed || node === parent.object;
+		}
 
 		// disregard the `bar` in `{ bar: foo }`, but keep it in `{ [bar]: foo }`
 		if ( parent.type === 'Property' ) return parent.computed || node === parent.value;
diff --git a/src/finalisers/iife.js b/src/finalisers/iife.js
index 95c6d65..1d4dfb2 100644
--- a/src/finalisers/iife.js
+++ b/src/finalisers/iife.js
@@ -31,7 +31,7 @@ export default function iife ( bundle, magicString, { exportMode, indentString }
 	}
 
 	if ( exportMode === 'named' ) {
-		dependencies.unshift( `(this.${name} = {})` );
+		dependencies.unshift( `(this.${name} = this.${name} || {})` );
 		args.unshift( 'exports' );
 	}
 
diff --git a/src/finalisers/umd.js b/src/finalisers/umd.js
index 3e8e813..e0d18e1 100644
--- a/src/finalisers/umd.js
+++ b/src/finalisers/umd.js
@@ -31,7 +31,7 @@ export default function umd ( bundle, magicString, { exportMode, indentString },
 	if ( exportMode === 'named' ) {
 		amdDeps.unshift( `'exports'` );
 		cjsDeps.unshift( `exports` );
-		globalDeps.unshift( `(${setupNamespace(options.moduleName)} = {})` );
+		globalDeps.unshift( `(${setupNamespace(options.moduleName)} = global.${options.moduleName} || {})` );
 
 		args.unshift( 'exports' );
 	}
diff --git a/src/utils/promise.js b/src/utils/promise.js
new file mode 100644
index 0000000..1730de8
--- /dev/null
+++ b/src/utils/promise.js
@@ -0,0 +1,16 @@
+import Promise from 'es6-promise/lib/es6-promise/promise.js';
+
+export function mapSequence ( array, fn ) {
+	let results = [];
+	let promise = Promise.resolve();
+
+	function next ( member, i ) {
+		return fn( member ).then( value => results[i] = value );
+	}
+
+	for ( let i = 0; i < array.length; i += 1 ) {
+		promise = promise.then( () => next( array[i], i ) );
+	}
+
+	return promise.then( () => results );
+}
diff --git a/src/utils/run.js b/src/utils/run.js
index 4470305..b57149d 100644
--- a/src/utils/run.js
+++ b/src/utils/run.js
@@ -95,6 +95,8 @@ export default function run ( node, scope, statement, strongDependencies, force
 
 				if ( declaration ) {
 					if ( declaration.isParam ) hasSideEffect = true;
+				} else if ( !scope.isTopLevel ) {
+					hasSideEffect = true;
 				} else {
 					declaration = statement.module.trace( subject.name );
 
diff --git a/test/form/computed-properties/_expected/amd.js b/test/form/computed-properties/_expected/amd.js
index 4fd933f..0ccd4d8 100644
--- a/test/form/computed-properties/_expected/amd.js
+++ b/test/form/computed-properties/_expected/amd.js
@@ -1,9 +1,19 @@
 define(['exports'], function (exports) { 'use strict';
 
 	var foo = 'foo';
+	var bar = 'bar';
+	var baz = 'baz';
+	var bam = 'bam';
 
-	var x = {[foo]: 'bar'};
+	var x = { [foo]: 'bar' };
+
+	class X {
+		[bar] () {}
+		get [baz] () {}
+		set [bam] ( value ) {}
+	}
 
 	exports.x = x;
+	exports.X = X;
 
 });
\ No newline at end of file
diff --git a/test/form/computed-properties/_expected/cjs.js b/test/form/computed-properties/_expected/cjs.js
index 22126d8..443bab3 100644
--- a/test/form/computed-properties/_expected/cjs.js
+++ b/test/form/computed-properties/_expected/cjs.js
@@ -1,7 +1,17 @@
 'use strict';
 
 var foo = 'foo';
+var bar = 'bar';
+var baz = 'baz';
+var bam = 'bam';
 
-var x = {[foo]: 'bar'};
+var x = { [foo]: 'bar' };
 
-exports.x = x;
\ No newline at end of file
+class X {
+	[bar] () {}
+	get [baz] () {}
+	set [bam] ( value ) {}
+}
+
+exports.x = x;
+exports.X = X;
\ No newline at end of file
diff --git a/test/form/computed-properties/_expected/es6.js b/test/form/computed-properties/_expected/es6.js
index 6dc09ca..d818b11 100644
--- a/test/form/computed-properties/_expected/es6.js
+++ b/test/form/computed-properties/_expected/es6.js
@@ -1,5 +1,14 @@
 var foo = 'foo';
+var bar = 'bar';
+var baz = 'baz';
+var bam = 'bam';
 
-var x = {[foo]: 'bar'};
+var x = { [foo]: 'bar' };
 
-export { x };
\ No newline at end of file
+class X {
+	[bar] () {}
+	get [baz] () {}
+	set [bam] ( value ) {}
+}
+
+export { x, X };
\ No newline at end of file
diff --git a/test/form/computed-properties/_expected/iife.js b/test/form/computed-properties/_expected/iife.js
index 35b80af..031368a 100644
--- a/test/form/computed-properties/_expected/iife.js
+++ b/test/form/computed-properties/_expected/iife.js
@@ -2,9 +2,19 @@
 	'use strict';
 
 	var foo = 'foo';
+	var bar = 'bar';
+	var baz = 'baz';
+	var bam = 'bam';
 
-	var x = {[foo]: 'bar'};
+	var x = { [foo]: 'bar' };
+
+	class X {
+		[bar] () {}
+		get [baz] () {}
+		set [bam] ( value ) {}
+	}
 
 	exports.x = x;
+	exports.X = X;
 
-}((this.computedProperties = {})));
\ No newline at end of file
+}((this.computedProperties = this.computedProperties || {})));
\ No newline at end of file
diff --git a/test/form/computed-properties/_expected/umd.js b/test/form/computed-properties/_expected/umd.js
index 5f7d146..ae57683 100644
--- a/test/form/computed-properties/_expected/umd.js
+++ b/test/form/computed-properties/_expected/umd.js
@@ -1,13 +1,23 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
 	typeof define === 'function' && define.amd ? define(['exports'], factory) :
-	(factory((global.computedProperties = {})));
+	(factory((global.computedProperties = global.computedProperties || {})));
 }(this, function (exports) { 'use strict';
 
 	var foo = 'foo';
+	var bar = 'bar';
+	var baz = 'baz';
+	var bam = 'bam';
 
-	var x = {[foo]: 'bar'};
+	var x = { [foo]: 'bar' };
+
+	class X {
+		[bar] () {}
+		get [baz] () {}
+		set [bam] ( value ) {}
+	}
 
 	exports.x = x;
+	exports.X = X;
 
 }));
\ No newline at end of file
diff --git a/test/form/computed-properties/main.js b/test/form/computed-properties/main.js
index 65bb97c..6cfc64a 100644
--- a/test/form/computed-properties/main.js
+++ b/test/form/computed-properties/main.js
@@ -1,3 +1,12 @@
 var foo = 'foo';
+var bar = 'bar';
+var baz = 'baz';
+var bam = 'bam';
 
-export var x = {[foo]: 'bar'};
+export var x = { [foo]: 'bar' };
+
+export class X {
+	[bar] () {}
+	get [baz] () {}
+	set [bam] ( value ) {}
+}
diff --git a/test/form/dedupes-external-imports/_expected/iife.js b/test/form/dedupes-external-imports/_expected/iife.js
index 17ed0b7..57e6649 100644
--- a/test/form/dedupes-external-imports/_expected/iife.js
+++ b/test/form/dedupes-external-imports/_expected/iife.js
@@ -30,4 +30,4 @@
 	exports.bar = bar;
 	exports.baz = baz;
 
-}((this.myBundle = {}),external));
+}((this.myBundle = this.myBundle || {}),external));
diff --git a/test/form/dedupes-external-imports/_expected/umd.js b/test/form/dedupes-external-imports/_expected/umd.js
index 70bc301..06be0e7 100644
--- a/test/form/dedupes-external-imports/_expected/umd.js
+++ b/test/form/dedupes-external-imports/_expected/umd.js
@@ -1,7 +1,7 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports, require('external')) :
 	typeof define === 'function' && define.amd ? define(['exports', 'external'], factory) :
-	(factory((global.myBundle = {}),global.external));
+	(factory((global.myBundle = global.myBundle || {}),global.external));
 }(this, function (exports,external) { 'use strict';
 
 	class Foo extends external.Component {
diff --git a/test/form/export-all-from-internal/_expected/iife.js b/test/form/export-all-from-internal/_expected/iife.js
index b5dad56..8a3cd17 100644
--- a/test/form/export-all-from-internal/_expected/iife.js
+++ b/test/form/export-all-from-internal/_expected/iife.js
@@ -7,4 +7,4 @@
 	exports.a = a;
 	exports.b = b;
 
-}((this.exposedInternals = {})));
+}((this.exposedInternals = this.exposedInternals || {})));
diff --git a/test/form/export-all-from-internal/_expected/umd.js b/test/form/export-all-from-internal/_expected/umd.js
index 74613b4..b249cc6 100644
--- a/test/form/export-all-from-internal/_expected/umd.js
+++ b/test/form/export-all-from-internal/_expected/umd.js
@@ -1,7 +1,7 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
 	typeof define === 'function' && define.amd ? define(['exports'], factory) :
-	(factory((global.exposedInternals = {})));
+	(factory((global.exposedInternals = global.exposedInternals || {})));
 }(this, function (exports) { 'use strict';
 
 	const a = 1;
diff --git a/test/form/exports-at-end-if-possible/_expected/iife.js b/test/form/exports-at-end-if-possible/_expected/iife.js
index a0ce6a9..1c5c67b 100644
--- a/test/form/exports-at-end-if-possible/_expected/iife.js
+++ b/test/form/exports-at-end-if-possible/_expected/iife.js
@@ -9,4 +9,4 @@
 
 	exports.FOO = FOO;
 
-}((this.myBundle = {})));
+}((this.myBundle = this.myBundle || {})));
diff --git a/test/form/exports-at-end-if-possible/_expected/umd.js b/test/form/exports-at-end-if-possible/_expected/umd.js
index 20d0d2a..e9cbc8d 100644
--- a/test/form/exports-at-end-if-possible/_expected/umd.js
+++ b/test/form/exports-at-end-if-possible/_expected/umd.js
@@ -1,7 +1,7 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
 	typeof define === 'function' && define.amd ? define(['exports'], factory) :
-	(factory((global.myBundle = {})));
+	(factory((global.myBundle = global.myBundle || {})));
 }(this, function (exports) { 'use strict';
 
 	var FOO = 'foo';
diff --git a/test/form/multiple-exports/_expected/iife.js b/test/form/multiple-exports/_expected/iife.js
index 3a3975d..d2da90f 100644
--- a/test/form/multiple-exports/_expected/iife.js
+++ b/test/form/multiple-exports/_expected/iife.js
@@ -7,4 +7,4 @@
 	exports.foo = foo;
 	exports.bar = bar;
 
-}((this.myBundle = {})));
+}((this.myBundle = this.myBundle || {})));
diff --git a/test/form/multiple-exports/_expected/umd.js b/test/form/multiple-exports/_expected/umd.js
index 485e381..30a54d6 100644
--- a/test/form/multiple-exports/_expected/umd.js
+++ b/test/form/multiple-exports/_expected/umd.js
@@ -1,7 +1,7 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
 	typeof define === 'function' && define.amd ? define(['exports'], factory) :
-	(factory((global.myBundle = {})));
+	(factory((global.myBundle = global.myBundle || {})));
 }(this, function (exports) { 'use strict';
 
 	var foo = 1;
diff --git a/test/form/namespaced-named-exports/_expected/iife.js b/test/form/namespaced-named-exports/_expected/iife.js
index 2fc75df..69637e9 100644
--- a/test/form/namespaced-named-exports/_expected/iife.js
+++ b/test/form/namespaced-named-exports/_expected/iife.js
@@ -7,4 +7,4 @@ this.foo.bar = this.foo.bar || {};
 
 	exports.answer = answer;
 
-}((this.foo.bar.baz = {})));
+}((this.foo.bar.baz = this.foo.bar.baz || {})));
diff --git a/test/form/namespaced-named-exports/_expected/umd.js b/test/form/namespaced-named-exports/_expected/umd.js
index aeb7775..9a0f47d 100644
--- a/test/form/namespaced-named-exports/_expected/umd.js
+++ b/test/form/namespaced-named-exports/_expected/umd.js
@@ -1,7 +1,7 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
 	typeof define === 'function' && define.amd ? define(['exports'], factory) :
-	(factory((global.foo = global.foo || {}, global.foo.bar = global.foo.bar || {}, global.foo.bar.baz = {})));
+	(factory((global.foo = global.foo || {}, global.foo.bar = global.foo.bar || {}, global.foo.bar.baz = global.foo.bar.baz || {})));
 }(this, function (exports) { 'use strict';
 
 	var answer = 42;
diff --git a/test/form/preserves-comments-after-imports/_expected/iife.js b/test/form/preserves-comments-after-imports/_expected/iife.js
index e9338dc..ee4c000 100644
--- a/test/form/preserves-comments-after-imports/_expected/iife.js
+++ b/test/form/preserves-comments-after-imports/_expected/iife.js
@@ -9,4 +9,4 @@
 
 	exports.obj = obj;
 
-}((this.myBundle = {})));
+}((this.myBundle = this.myBundle || {})));
diff --git a/test/form/preserves-comments-after-imports/_expected/umd.js b/test/form/preserves-comments-after-imports/_expected/umd.js
index ac58856..13a54bf 100644
--- a/test/form/preserves-comments-after-imports/_expected/umd.js
+++ b/test/form/preserves-comments-after-imports/_expected/umd.js
@@ -1,7 +1,7 @@
 (function (global, factory) {
 	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
 	typeof define === 'function' && define.amd ? define(['exports'], factory) :
-	(factory((global.myBundle = {})));
+	(factory((global.myBundle = global.myBundle || {})));
 }(this, function (exports) { 'use strict';
 
 	/** A comment for a number */
diff --git a/test/function/empty-exports/_config.js b/test/function/empty-exports/_config.js
new file mode 100644
index 0000000..65b2185
--- /dev/null
+++ b/test/function/empty-exports/_config.js
@@ -0,0 +1,17 @@
+var assert = require( 'assert' );
+
+var warned = false;
+
+module.exports = {
+	description: 'warns on export {}, but does not fail',
+	options: {
+		onwarn: function ( msg ) {
+			warned = true;
+			assert.ok( /main\.js has an empty export declaration/.test( msg ) );
+		}
+	},
+	exports: function ( exports ) {
+		assert.equal( Object.keys( exports ).length, 0 );
+		assert.ok( warned, 'did not warn' );
+	}
+};
diff --git a/test/function/empty-exports/main.js b/test/function/empty-exports/main.js
new file mode 100644
index 0000000..cb0ff5c
--- /dev/null
+++ b/test/function/empty-exports/main.js
@@ -0,0 +1 @@
+export {};
diff --git a/test/function/member-expression-assignment-in-function/_config.js b/test/function/member-expression-assignment-in-function/_config.js
new file mode 100644
index 0000000..bf7e6fc
--- /dev/null
+++ b/test/function/member-expression-assignment-in-function/_config.js
@@ -0,0 +1,10 @@
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'detect side effect in member expression assignment when not top level',
+	code: function ( code ) {
+		assert.equal( code.indexOf( 'function set(key, value) { foo[key] = value; }' ) >= 0, true, code );
+		assert.equal( code.indexOf( 'set("bar", 2);' ) >= 0, true, code );
+		assert.equal( code.indexOf( 'set("qux", 3);' ) >= 0, true, code );
+	}
+}
diff --git a/test/function/member-expression-assignment-in-function/main.js b/test/function/member-expression-assignment-in-function/main.js
new file mode 100644
index 0000000..f627721
--- /dev/null
+++ b/test/function/member-expression-assignment-in-function/main.js
@@ -0,0 +1,9 @@
+var foo = {};
+
+function set(key, value) { foo[key] = value; }
+
+set("bar", 2);
+set("qux", 3);
+
+console.log(foo);
+