diff --git a/src/Declaration.js b/src/Declaration.js
index a8e192a..0601606 100644
--- a/src/Declaration.js
+++ b/src/Declaration.js
@@ -282,7 +282,7 @@ export class ExternalDeclaration {
 		}
 
 		if ( this.name === 'default' ) {
-			return !es6 && this.module.exportsNames ?
+			return this.module.exportsNamespace || ( !es6 && this.module.exportsNames ) ?
 				`${this.module.name}__default` :
 				this.module.name;
 		}
diff --git a/src/ExternalModule.js b/src/ExternalModule.js
index 3113a5d..db9c062 100644
--- a/src/ExternalModule.js
+++ b/src/ExternalModule.js
@@ -27,9 +27,8 @@ export default class ExternalModule {
 	}
 
 	traceExport ( name ) {
-		if ( name !== 'default' && name !== '*' ) {
-			this.exportsNames = true;
-		}
+		if ( name !== 'default' && name !== '*' ) this.exportsNames = true;
+		if ( name === '*' ) this.exportsNamespace = true;
 
 		return this.declarations[ name ] || (
 			this.declarations[ name ] = new ExternalDeclaration( this, name )
diff --git a/src/finalisers/cjs.js b/src/finalisers/cjs.js
index b921429..ecb57ea 100644
--- a/src/finalisers/cjs.js
+++ b/src/finalisers/cjs.js
@@ -3,11 +3,12 @@ import getExportBlock from './shared/getExportBlock.js';
 export default function cjs ( bundle, magicString, { exportMode }, options ) {
 	let intro = options.useStrict === false ? `` : `'use strict';\n\n`;
 
-	const hasDefaultImport = bundle.externalModules.some( mod => mod.declarations.default);
+	let needsInterop = false;
+	// const hasDefaultImport = bundle.externalModules.some( mod => mod.declarations.default);
 
-	if (hasDefaultImport) {
-		intro += `function _interopDefault (ex) { return (ex && (typeof ex === 'object') && 'default' in ex) ? ex['default'] : ex; }\n\n`;
-	}
+	// if (hasDefaultImport) {
+	// 	intro += `function _interopDefault (ex) { return (ex && (typeof ex === 'object') && 'default' in ex) ? ex['default'] : ex; }\n\n`;
+	// }
 
 	const varOrConst = bundle.varOrConst;
 
@@ -15,18 +16,29 @@ export default function cjs ( bundle, magicString, { exportMode }, options ) {
 	const importBlock = bundle.externalModules
 		.map( module => {
 			if ( module.declarations.default ) {
-				if (module.exportsNames) {
+				if ( module.exportsNamespace ) {
+					return `${varOrConst} ${module.name} = require('${module.id}');` +
+						`\n${varOrConst} ${module.name}__default = ${module.name}['default'];`;
+				}
+
+				needsInterop = true;
+
+				if ( module.exportsNames ) {
 					return `${varOrConst} ${module.name} = require('${module.id}');` +
 						`\n${varOrConst} ${module.name}__default = _interopDefault(${module.name});`;
-				} else {
-					return `${varOrConst} ${module.name} = _interopDefault(require('${module.id}'));`;
 				}
+
+				return `${varOrConst} ${module.name} = _interopDefault(require('${module.id}'));`;
 			} else {
 				return `${varOrConst} ${module.name} = require('${module.id}');`;
 			}
 		})
 		.join( '\n' );
 
+	if ( needsInterop ) {
+		intro += `function _interopDefault (ex) { return (ex && (typeof ex === 'object') && 'default' in ex) ? ex['default'] : ex; }\n\n`;
+	}
+
 	if ( importBlock ) {
 		intro += importBlock + '\n\n';
 	}
diff --git a/src/finalisers/es6.js b/src/finalisers/es6.js
index a86e04e..bd3f93f 100644
--- a/src/finalisers/es6.js
+++ b/src/finalisers/es6.js
@@ -19,7 +19,11 @@ export default function es6 ( bundle, magicString ) {
 				});
 
 			if ( module.declarations.default ) {
-				specifiers.push( module.name );
+				if ( module.exportsNamespace ) {
+					specifiersList.push([ `${module.name}__default` ]);
+				} else {
+					specifiers.push( module.name );
+				}
 			}
 
 			const namespaceSpecifier = module.declarations['*'] ? `* as ${module.name}` : null;
diff --git a/src/finalisers/shared/getInteropBlock.js b/src/finalisers/shared/getInteropBlock.js
index a747d82..67a26d7 100644
--- a/src/finalisers/shared/getInteropBlock.js
+++ b/src/finalisers/shared/getInteropBlock.js
@@ -1,11 +1,17 @@
 export default function getInteropBlock ( bundle ) {
 	return bundle.externalModules
 		.map( module => {
-			return module.declarations.default ?
-				( module.exportsNames ?
-					`${bundle.varOrConst} ${module.name}__default = 'default' in ${module.name} ? ${module.name}['default'] : ${module.name};` :
-					`${module.name} = 'default' in ${module.name} ? ${module.name}['default'] : ${module.name};` ) :
-				null;
+			if ( !module.declarations.default ) return null;
+
+			if ( module.exportsNamespace ) {
+				return `${bundle.varOrConst} ${module.name}__default = ${module.name}['default'];`;
+			}
+
+			if ( module.exportsNames ) {
+				return `${bundle.varOrConst} ${module.name}__default = 'default' in ${module.name} ? ${module.name}['default'] : ${module.name};`;
+			}
+
+			return `${module.name} = 'default' in ${module.name} ? ${module.name}['default'] : ${module.name};`;
 		})
 		.filter( Boolean )
 		.join( '\n' );
diff --git a/test/form/import-external-namespace-and-default/_config.js b/test/form/import-external-namespace-and-default/_config.js
new file mode 100644
index 0000000..5ee7b48
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'disinguishes between external default and namespace (#637)'
+};
diff --git a/test/form/import-external-namespace-and-default/_expected/amd.js b/test/form/import-external-namespace-and-default/_expected/amd.js
new file mode 100644
index 0000000..1f4b3f9
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/_expected/amd.js
@@ -0,0 +1,9 @@
+define(['foo'], function (foo) { 'use strict';
+
+	var foo__default = foo['default'];
+
+	console.log( foo.bar );
+
+	console.log( foo__default );
+
+});
diff --git a/test/form/import-external-namespace-and-default/_expected/cjs.js b/test/form/import-external-namespace-and-default/_expected/cjs.js
new file mode 100644
index 0000000..14c733e
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/_expected/cjs.js
@@ -0,0 +1,8 @@
+'use strict';
+
+var foo = require('foo');
+var foo__default = foo['default'];
+
+console.log( foo.bar );
+
+console.log( foo__default );
diff --git a/test/form/import-external-namespace-and-default/_expected/es6.js b/test/form/import-external-namespace-and-default/_expected/es6.js
new file mode 100644
index 0000000..5655595
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/_expected/es6.js
@@ -0,0 +1,6 @@
+import * as foo from 'foo';
+import foo__default from 'foo';
+
+console.log( foo.bar );
+
+console.log( foo__default );
diff --git a/test/form/import-external-namespace-and-default/_expected/iife.js b/test/form/import-external-namespace-and-default/_expected/iife.js
new file mode 100644
index 0000000..b2c5788
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/_expected/iife.js
@@ -0,0 +1,10 @@
+(function (foo) {
+	'use strict';
+
+	var foo__default = foo['default'];
+
+	console.log( foo.bar );
+
+	console.log( foo__default );
+
+}(foo));
diff --git a/test/form/import-external-namespace-and-default/_expected/umd.js b/test/form/import-external-namespace-and-default/_expected/umd.js
new file mode 100644
index 0000000..ddcdcbd
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/_expected/umd.js
@@ -0,0 +1,13 @@
+(function (global, factory) {
+	typeof exports === 'object' && typeof module !== 'undefined' ? factory(require('foo')) :
+	typeof define === 'function' && define.amd ? define(['foo'], factory) :
+	(factory(global.foo));
+}(this, function (foo) { 'use strict';
+
+	var foo__default = foo['default'];
+
+	console.log( foo.bar );
+
+	console.log( foo__default );
+
+}));
diff --git a/test/form/import-external-namespace-and-default/main.js b/test/form/import-external-namespace-and-default/main.js
new file mode 100644
index 0000000..719a96a
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/main.js
@@ -0,0 +1,4 @@
+import foo from 'foo';
+import './other.js';
+
+console.log( foo );
diff --git a/test/form/import-external-namespace-and-default/other.js b/test/form/import-external-namespace-and-default/other.js
new file mode 100644
index 0000000..8149fb6
--- /dev/null
+++ b/test/form/import-external-namespace-and-default/other.js
@@ -0,0 +1,3 @@
+import * as foo from 'foo';
+
+console.log( foo.bar );