diff --git a/src/index.js b/src/index.js
index 6717d36c..3cd0df76 100644
--- a/src/index.js
+++ b/src/index.js
@@ -2,6 +2,8 @@
   MIT License http://www.opensource.org/licenses/mit-license.php
   Author Tobias Koppers @sokra
 */
+import path from 'path';
+
 import { getOptions, isUrlRequest } from 'loader-utils';
 import postcss from 'postcss';
 import postcssPkg from 'postcss/package.json';
@@ -87,6 +89,15 @@ export default function loader(content, map, meta) {
         : false,
     })
     .then((result) => {
+      // work-around for apparent bug in postcss that loses the paths to source
+      // files in existing map previously generated by postcss-loader:
+      if (result.map && map && map.file) {
+        /* eslint-disable no-underscore-dangle, no-param-reassign */
+        result.map._sourceRoot = path.dirname(map.file);
+        result.map._file = map.file;
+        /* eslint-enable */
+      }
+
       result
         .warnings()
         .forEach((warning) => this.emitWarning(new Warning(warning)));