diff --git a/src/index.js b/src/index.js
index d789813..596fa59 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,12 +1,7 @@
-import { posix as path } from 'path';
-import { platform } from 'os';
+import path from 'path';
 import fs from 'fs';
-
 import slash from 'slash';
 
-const VOLUME = /^([A-Z]:)/;
-const IS_WINDOWS = platform() === 'win32';
-
 // Helper functions
 const noop = () => null;
 const matches = (key, importee) => {
@@ -21,7 +16,8 @@ const matches = (key, importee) => {
   return importeeStartsWithKey && importeeHasSlashAfterKey;
 };
 const endsWith = (needle, haystack) => haystack.slice(-needle.length) === needle;
-const isFilePath = id => /^\.?\//.test(id);
+const isAbsolutePath = id => /^(?:\/|(?:[A-Za-z]:)?[\\\/])/.test(id);
+const isRelativePath = id => /^\.?\.[\\\/]/.test(id);
 const exists = uri => {
   try {
     return fs.statSync(uri).isFile();
@@ -29,10 +25,9 @@ const exists = uri => {
     return false;
   }
 };
-
 const normalizeId = id => {
-  if (IS_WINDOWS && typeof id === 'string') {
-    return slash(id.replace(VOLUME, ''));
+  if (typeof id === 'string') {
+    return slash(id);
   }
 
   return id;
@@ -63,29 +58,35 @@ export default function alias(options = {}) {
         return null;
       }
 
-      const entry = options[toReplace];
+      const entry = normalizeId(options[toReplace]);
 
       const updatedId = importeeId.replace(toReplace, entry);
 
-      if (isFilePath(updatedId)) {
-        const directory = path.dirname(importerId);
+      if (isRelativePath(updatedId) || isAbsolutePath(updatedId)) {
+        let filePath;
+        if (isRelativePath(updatedId) && importer === undefined) {
+          // Cannot handle this, so return null
+          return null;
+        } else if (isRelativePath(updatedId) && importer !== undefined) {
+          // Resolve file names
+          filePath = path.resolve(path.dirname(importerId), updatedId);
+        } else {
+          // Absolute path doesn't need resolve
+          filePath = updatedId;
+        }
 
-        // Resolve file names
-        const filePath = path.resolve(directory, updatedId);
         const match = resolve.map(ext => `${filePath}${ext}`)
                             .find(exists);
 
         if (match) {
-          return match;
-        }
-
-        // To keep the previous behaviour we simply return the file path
-        // with extension
-        if (endsWith('.js', filePath)) {
-          return filePath;
+          filePath = match;
+        } else if (!endsWith('.js', filePath)) {
+          // To keep the previous behaviour we simply return the file path
+          // with extension
+          filePath = filePath + '.js';
         }
 
-        return filePath + '.js';
+        return normalizeId(filePath);
       }
 
       return updatedId;
diff --git a/test/index.js b/test/index.js
index 01cecb9..94b0dc5 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,10 +1,10 @@
 import test from 'ava';
-import { posix as path } from 'path';
+import path from 'path';
 import { rollup } from 'rollup';
 import alias from '../dist/rollup-plugin-alias';
 import slash from 'slash';
 
-const DIRNAME = slash(__dirname.replace(/^([A-Z]:)/, ''));
+const normalizeId = id => slash(id);
 
 test(t => {
   t.is(typeof alias, 'function');
@@ -29,9 +29,9 @@ test('Simple aliasing', t => {
     './local': 'global',
   });
 
-  const resolved = result.resolveId('foo', '/src/importer.js');
-  const resolved2 = result.resolveId('pony', '/src/importer.js');
-  const resolved3 = result.resolveId('./local', '/src/importer.js');
+  const resolved = result.resolveId('foo', path.resolve('/src/importer.js'));
+  const resolved2 = result.resolveId('pony', path.resolve('/src/importer.js'));
+  const resolved3 = result.resolveId('./local', path.resolve('/src/importer.js'));
 
   t.is(resolved, 'bar');
   t.is(resolved2, 'paradise');
@@ -44,47 +44,64 @@ test('Will not confuse modules with similar names', t => {
     './foo': 'bar',
   });
 
-  const resolved = result.resolveId('foo2', '/src/importer.js');
-  const resolved2 = result.resolveId('./fooze/bar', '/src/importer.js');
-  const resolved3 = result.resolveId('./someFile.foo', '/src/importer.js');
+  const resolved = result.resolveId('foo2', path.resolve('/src/importer.js'));
+  const resolved2 = result.resolveId('./fooze/bar', path.resolve('/src/importer.js'));
+  const resolved3 = result.resolveId('./someFile.foo', path.resolve('/src/importer.js'));
 
   t.is(resolved, null);
   t.is(resolved2, null);
   t.is(resolved3, null);
 });
 
-test('Local aliasing', t => {
+test('Local aliasing with POSIX path', t => {
   const result = alias({
     foo: './bar',
     pony: './par/a/di/se',
   });
 
-  const resolved = result.resolveId('foo', '/src/importer.js');
-  const resolved2 = result.resolveId('foo/baz', '/src/importer.js');
-  const resolved3 = result.resolveId('foo/baz.js', '/src/importer.js');
-  const resolved4 = result.resolveId('pony', '/src/highly/nested/importer.js');
+  const resolved = result.resolveId('foo', path.resolve('/src/importer.js'));
+  const resolved2 = result.resolveId('foo/baz', path.resolve('/src/importer.js'));
+  const resolved3 = result.resolveId('foo/baz.js', path.resolve('/src/importer.js'));
+  const resolved4 = result.resolveId('pony', path.resolve('/src/highly/nested/importer.js'));
 
-  t.is(resolved, '/src/bar.js');
-  t.is(resolved2, '/src/bar/baz.js');
-  t.is(resolved3, '/src/bar/baz.js');
-  t.is(resolved4, '/src/highly/nested/par/a/di/se.js');
+  t.is(resolved, normalizeId(path.resolve('/src/bar.js')));
+  t.is(resolved2, normalizeId(path.resolve('/src/bar/baz.js')));
+  t.is(resolved3, normalizeId(path.resolve('/src/bar/baz.js')));
+  t.is(resolved4, normalizeId(path.resolve('/src/highly/nested/par/a/di/se.js')));
+});
+
+test('Local aliasing with Windows path', t => {
+  const result = alias({
+    foo: '.\\bar',
+    pony: '.\\par\\a\\di\\se',
+  });
+
+  const resolved = result.resolveId('foo', path.resolve('/src/importer.js'));
+  const resolved2 = result.resolveId('foo/baz', path.resolve('/src/importer.js'));
+  const resolved3 = result.resolveId('foo/baz.js', path.resolve('/src/importer.js'));
+  const resolved4 = result.resolveId('pony', path.resolve('/src/highly/nested/importer.js'));
+
+  t.is(resolved, normalizeId(path.resolve('/src/bar.js')));
+  t.is(resolved2, normalizeId(path.resolve('/src/bar/baz.js')));
+  t.is(resolved3, normalizeId(path.resolve('/src/bar/baz.js')));
+  t.is(resolved4, normalizeId(path.resolve('/src/highly/nested/par/a/di/se.js')));
 });
 
 test('Absolute local aliasing', t => {
   const result = alias({
-    foo: '/bar',
-    pony: '/par/a/di/se.js',
+    foo: path.resolve('/bar'),
+    pony: path.resolve('/par/a/di/se.js'),
   });
 
-  const resolved = result.resolveId('foo', '/src/importer.js');
-  const resolved2 = result.resolveId('foo/baz', '/src/importer.js');
-  const resolved3 = result.resolveId('foo/baz.js', '/src/importer.js');
-  const resolved4 = result.resolveId('pony', '/src/highly/nested/importer.js');
+  const resolved = result.resolveId('foo', path.resolve('/src/importer.js'));
+  const resolved2 = result.resolveId('foo/baz', path.resolve('/src/importer.js'));
+  const resolved3 = result.resolveId('foo/baz.js', path.resolve('/src/importer.js'));
+  const resolved4 = result.resolveId('pony', path.resolve('/src/highly/nested/importer.js'));
 
-  t.is(resolved, '/bar.js');
-  t.is(resolved2, '/bar/baz.js');
-  t.is(resolved3, '/bar/baz.js');
-  t.is(resolved4, '/par/a/di/se.js');
+  t.is(resolved, normalizeId(path.resolve('/bar.js')));
+  t.is(resolved2, normalizeId(path.resolve('/bar/baz.js')));
+  t.is(resolved3, normalizeId(path.resolve('/bar/baz.js')));
+  t.is(resolved4, normalizeId(path.resolve('/par/a/di/se.js')));
 });
 
 test('Test for the resolve property', t => {
@@ -93,9 +110,9 @@ test('Test for the resolve property', t => {
     resolve: ['.js', '.jsx'],
   });
 
-  const resolved = result.resolveId('ember', path.resolve(DIRNAME, './files/index.js'));
+  const resolved = result.resolveId('ember', path.resolve(__dirname, './files/index.js'));
 
-  t.is(resolved, path.resolve(DIRNAME, './files/folder/hipster.jsx'));
+  t.is(resolved, normalizeId(path.resolve(__dirname, './files/folder/hipster.jsx')));
 });
 
 test(t => {
@@ -103,7 +120,7 @@ test(t => {
     resolve: 'i/am/a/file',
   });
 
-  const resolved = result.resolveId('resolve', '/src/import.js');
+  const resolved = result.resolveId('resolve', path.resolve('/src/import.js'));
 
   t.is(resolved, 'i/am/a/file');
 });
@@ -113,9 +130,9 @@ test(t => {
     resolve: './i/am/a/local/file',
   });
 
-  const resolved = result.resolveId('resolve', path.resolve(DIRNAME, './files/index.js'));
+  const resolved = result.resolveId('resolve', path.resolve(__dirname, './files/index.js'));
 
-  t.is(resolved, path.resolve(DIRNAME, './files/i/am/a/local/file.js'));
+  t.is(resolved, normalizeId(path.resolve(__dirname, './files/i/am/a/local/file.js')));
 });
 
 // Tests in Rollup
@@ -129,11 +146,37 @@ test(t =>
       './numberFolder': './folder',
     })],
   }).then(stats => {
-    t.is(stats.modules[0].id.endsWith('/files/nonAliased.js'), true);
-    t.is(stats.modules[1].id.endsWith('/files/aliasMe.js'), true);
-    t.is(stats.modules[2].id.endsWith('/files/localAliasMe.js'), true);
-    t.is(stats.modules[3].id.endsWith('/files/folder/anotherNumber.js'), true);
-    t.is(stats.modules[4].id.endsWith('/files/index.js'), true);
+    t.is(stats.modules[0].id, normalizeId(path.resolve('./files/nonAliased.js')));
+    t.is(stats.modules[1].id, normalizeId(path.resolve('./files/aliasMe.js')));
+    t.is(stats.modules[2].id, normalizeId(path.resolve('./files/localAliasMe.js')));
+    t.is(stats.modules[3].id, normalizeId(path.resolve('./files/folder/anotherNumber.js')));
+    t.is(stats.modules[4].id, normalizeId(path.resolve('./files/index.js')));
     t.is(stats.modules.length, 5);
   })
 );
+
+test('Relative local aliasing in rollup entry', t =>
+  rollup({
+    entry: 'src/aliasMe.js',
+    plugins: [alias({
+      src: './files',
+    })],
+  }).then(() => {
+    t.fail();
+  }).catch(() => {
+    t.pass();
+  })
+);
+
+test('Absolute local aliasing in rollup entry', t =>
+  rollup({
+    entry: 'src/aliasMe.js',
+    plugins: [alias({
+      src: path.resolve('./files'),
+    })],
+  }).then(() => {
+    t.pass();
+  }).catch(() => {
+    t.fail();
+  })
+);