diff --git a/package.json b/package.json
index cd9c282..e86f4fd 100644
--- a/package.json
+++ b/package.json
@@ -47,6 +47,7 @@
     "http-server": "0.9.0",
     "istanbul": "0.X",
     "jshint": "2.X",
+    "lodash": "4.17.4",
     "object-assign": "^4.1.0",
     "tape": "4.X"
   },
diff --git a/src/write/index.internals.js b/src/write/index.internals.js
index 324dac7..4c6040b 100644
--- a/src/write/index.internals.js
+++ b/src/write/index.internals.js
@@ -39,10 +39,18 @@ module.exports = function(destPath, options) {
 
     file.sourceMap.sources = file.sourceMap.sources.map(function(filePath) {
       // keep the references files like ../node_modules within the sourceRoot
+      debug(utils.logCb("filePath: " + filePath));
+      debug(utils.logCb("file.path: " + file.path));
+      debug(utils.logCb("file.cwd: " + file.cwd));
+      debug(utils.logCb("file.base: " + file.base));
+
       if (!file.dirname){
-        filePath = file.path.replace(file.cwd, '');
-      } else
-          filePath = path.resolve(file.dirname || '', filePath).replace(file.cwd, '');
+        debug(utils.logCb('!file.dirname'));
+        filePath = path.join(file.base, filePath).replace(file.cwd, '');
+      } else {
+          debug(utils.logCb('file.dirname: ' + file.dirname));
+          filePath = path.resolve(file.dirname, filePath).replace(file.cwd, '');
+      }
 
       return unixStylePath(filePath);
     });
diff --git a/test/assets/test3.js b/test/assets/test3.js
new file mode 100644
index 0000000..fea131c
--- /dev/null
+++ b/test/assets/test3.js
@@ -0,0 +1 @@
+console.log('three');
diff --git a/test/assets/test4.js b/test/assets/test4.js
new file mode 100644
index 0000000..a029dfe
--- /dev/null
+++ b/test/assets/test4.js
@@ -0,0 +1 @@
+console.log('four');
diff --git a/test/integration.js b/test/integration.js
index c0e279f..a7606b9 100644
--- a/test/integration.js
+++ b/test/integration.js
@@ -8,6 +8,7 @@ var debug = require('debug-fabulous')()(PLUGIN_NAME + ':test:integration');
 var join = require('path').join;
 var fs = require('fs');
 var sourceContent = fs.readFileSync(join(__dirname, 'assets/helloworld.js')).toString();
+var _ = require('lodash');
 
 
 function base64JSON(object) {
@@ -229,3 +230,31 @@ test('combined: mapped preExisting with two tasks', function(t) {
     });
   });
 });
+
+// - thanks @twiggy https://github.com/floridoo/gulp-sourcemaps/issues/270#issuecomment-271723208
+test('sources: is valid with concat', function(t) {
+
+  gulp.src([
+    join(__dirname, './assets/test3.js'),
+    join(__dirname, './assets/test4.js'),
+  ])
+  .pipe(sourcemaps.init())
+  .pipe($.concat("index.js"))
+  .pipe(sourcemaps.write('.'))
+  .pipe(gulp.dest('tmp/sources_concat'))
+  .on('data', function(file) {
+    if (!/.*\.map/.test(file.path)) return;
+
+    var contents = JSON.parse(file.contents.toString());
+    _.each(contents.sources, function(s, i){
+      t.deepEqual(s, "/test/assets/test" + (i+3) + ".js", "source is correct, test" + (i+3) + ".js");
+    });
+  })
+  .on('error', function() {
+    t.fail('emitted error');
+    t.end();
+  }).on('finish', function(){
+    moveHtml('sources_concat', t);
+  });
+
+});