Predefine the 'exports' global, and bind locals to found globals.

src/Bundle.js

@@ -32,6 +32,12 @@ export default class Bundle {
 		// The global scope, and the bundle's internal scope.
 		this.globals = new Scope();
 		this.scope = new Scope( this.globals );
+
+		// TODO strictly speaking, this only applies with non-ES6, non-default-only bundles
+		// However, the deconfliction logic is greatly simplified by being the same for all formats.
+		this.globals.define( 'exports' );
+		this.scope.bind( 'exports', this.globals.reference( 'exports' ) );
+
 		// Alias for entryModule.exports.
 		this.exports = null;
 
@@ -44,9 +50,6 @@ export default class Bundle {
 		this.statements = null;
 		this.externalModules = [];
 		this.internalNamespaceModules = [];
-
-		this.assumedGlobals = blank();
-		this.assumedGlobals.exports = true; // TODO strictly speaking, this only applies with non-ES6, non-default-only bundles
 	}
 
 	build () {

src/Module.js

@@ -254,6 +254,7 @@ export default class Module {
 			keys( statement.dependsOn ).forEach( name => {
 				if ( !this.locals.inScope( name ) ) {
 					this.bundle.globals.define( name );
+					this.locals.bind( name, this.bundle.globals.reference( name ) );
 				}
 			});
 		});
@@ -533,7 +534,9 @@ export default class Module {
 					.forEach( name => {
 						const id = this.locals.lookup( name );
 
-						if ( id.module && id.module.isExternal ) {
+						// HACK: We check that `id` isn't its own module,
+						// since that is the case for external defaults.
+						if ( id.module && id !== id.module && id.module.isExternal ) {
 							replacements[ name ] = `${id.module.name}.${id.originalName}`;
 						}
 					});