diff --git a/src/Bundle.js b/src/Bundle.js
index f5fedc8..d91479f 100644
--- a/src/Bundle.js
+++ b/src/Bundle.js
@@ -167,6 +167,12 @@ export default class Bundle {
 				msg += `: ${err.message}`;
 				throw new Error( msg );
 			})
+			.then( source => {
+				if ( typeof source === 'string' ) return source;
+				if ( source && typeof source === 'object' && source.code ) return source;
+
+				throw new Error( `Error loading ${id}: load hook should return a string, a { code, map } object, or nothing/null` );
+			})
 			.then( source => transform( source, id, this.transformers ) )
 			.then( source => {
 				const { code, originalCode, ast, sourceMapChain } = source;
diff --git a/src/ast/attachScopes.js b/src/ast/attachScopes.js
index 92798e8..51fc28a 100644
--- a/src/ast/attachScopes.js
+++ b/src/ast/attachScopes.js
@@ -29,7 +29,7 @@ export default function attachScopes ( statement ) {
 			let newScope;
 
 			// create new function scope
-			if ( /Function/.test( node.type ) ) {
+			if ( /(Function|Class)/.test( node.type ) ) {
 				newScope = new Scope({
 					parent: scope,
 					block: false,
@@ -38,7 +38,7 @@ export default function attachScopes ( statement ) {
 
 				// named function expressions - the name is considered
 				// part of the function's scope
-				if ( node.type === 'FunctionExpression' && node.id ) {
+				if ( /(Function|Class)Expression/.test( node.type ) && node.id ) {
 					newScope.addDeclaration( node, false, false );
 				}
 			}
diff --git a/test/form/assignment-to-exports-class-declaration/_config.js b/test/form/assignment-to-exports-class-declaration/_config.js
new file mode 100644
index 0000000..0f3d2ef
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/_config.js
@@ -0,0 +1,6 @@
+module.exports = {
+	description: 'does not rewrite class declaration IDs',
+	options: {
+		moduleName: 'myModule'
+	}
+};
diff --git a/test/form/assignment-to-exports-class-declaration/_expected/amd.js b/test/form/assignment-to-exports-class-declaration/_expected/amd.js
new file mode 100644
index 0000000..c2d0691
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/_expected/amd.js
@@ -0,0 +1,6 @@
+define(['exports'], function (exports) { 'use strict';
+
+	exports.Foo = class Foo {}
+	exports.Foo = lol( exports.Foo );
+
+});
diff --git a/test/form/assignment-to-exports-class-declaration/_expected/cjs.js b/test/form/assignment-to-exports-class-declaration/_expected/cjs.js
new file mode 100644
index 0000000..b062474
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/_expected/cjs.js
@@ -0,0 +1,4 @@
+'use strict';
+
+exports.Foo = class Foo {}
+exports.Foo = lol( exports.Foo );
diff --git a/test/form/assignment-to-exports-class-declaration/_expected/es6.js b/test/form/assignment-to-exports-class-declaration/_expected/es6.js
new file mode 100644
index 0000000..08e82c9
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/_expected/es6.js
@@ -0,0 +1,4 @@
+Foo = class Foo {}
+Foo = lol( Foo );
+
+export { Foo };
\ No newline at end of file
diff --git a/test/form/assignment-to-exports-class-declaration/_expected/iife.js b/test/form/assignment-to-exports-class-declaration/_expected/iife.js
new file mode 100644
index 0000000..fa37538
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/_expected/iife.js
@@ -0,0 +1,7 @@
+(function (exports) {
+	'use strict';
+
+	exports.Foo = class Foo {}
+	exports.Foo = lol( exports.Foo );
+
+}((this.myModule = this.myModule || {})));
diff --git a/test/form/assignment-to-exports-class-declaration/_expected/umd.js b/test/form/assignment-to-exports-class-declaration/_expected/umd.js
new file mode 100644
index 0000000..bbefc87
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/_expected/umd.js
@@ -0,0 +1,10 @@
+(function (global, factory) {
+	typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
+	typeof define === 'function' && define.amd ? define(['exports'], factory) :
+	(factory((global.myModule = global.myModule || {})));
+}(this, function (exports) { 'use strict';
+
+	exports.Foo = class Foo {}
+	exports.Foo = lol( exports.Foo );
+
+}));
diff --git a/test/form/assignment-to-exports-class-declaration/main.js b/test/form/assignment-to-exports-class-declaration/main.js
new file mode 100644
index 0000000..ceae376
--- /dev/null
+++ b/test/form/assignment-to-exports-class-declaration/main.js
@@ -0,0 +1,2 @@
+export let Foo = class Foo {}
+Foo = lol( Foo );
diff --git a/test/function/load-returns-string-or-null/_config.js b/test/function/load-returns-string-or-null/_config.js
new file mode 100644
index 0000000..ea80699
--- /dev/null
+++ b/test/function/load-returns-string-or-null/_config.js
@@ -0,0 +1,15 @@
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'throws error if load returns something wacky',
+	options: {
+		plugins: [{
+			load: function () {
+				return 42;
+			}
+		}]
+	},
+	error: function ( err ) {
+		assert.ok( /load hook should return a string, a \{ code, map \} object, or nothing\/null/.test( err.message ) );
+	}
+};