diff --git a/src/core/importType.js b/src/core/importType.js
index df60575c01..f59b687c87 100644
--- a/src/core/importType.js
+++ b/src/core/importType.js
@@ -29,10 +29,11 @@ function isExternalPath(path, name, settings) {
 }
 
 function isSubpath(subpath, path) {
-  const normSubpath = subpath.replace(/[/]$/, '')
+  const normSubpath = subpath.replace(/\/$/, '')
   if (normSubpath.length === 0) {
     return false
   }
+  path = path.replace(/\\/g, '/')
   const left = path.indexOf(normSubpath)
   const right = left + normSubpath.length
   return left !== -1 &&
diff --git a/tests/src/core/importType.js b/tests/src/core/importType.js
index 75be3101ed..59050c6782 100644
--- a/tests/src/core/importType.js
+++ b/tests/src/core/importType.js
@@ -1,7 +1,7 @@
 import { expect } from 'chai'
 import * as path from 'path'
 
-import importType from 'core/importType'
+import importType, {isExternalModule} from 'core/importType'
 
 import { testContext, testFilePath } from '../utils'
 
@@ -224,4 +224,8 @@ describe('importType(name)', function () {
     })
     expect(importType('@test-scope/some-module', foldersContext)).to.equal('external')
   })
+
+  it('`isExternalModule` should work with windows directory separator', function() {
+    expect(isExternalModule('foo', {}, 'E:\\path\\to\\node_modules\\foo')).to.equal(true)
+  })
 })