diff --git a/src/writeFile.js b/src/writeFile.js
index 43c86d6b..3abff673 100644
--- a/src/writeFile.js
+++ b/src/writeFile.js
@@ -26,6 +26,8 @@ export default function writeFile(globalRef, pattern, file) {
                 content = pattern.transform(content, file.absoluteFrom);
             }
 
+            return content;
+        }).then((content) => {
             var hash = loaderUtils.getHashDigest(content);
 
             if (pattern.toType === 'template') {
diff --git a/tests/index.js b/tests/index.js
index 3c5b9ed0..cb66a021 100644
--- a/tests/index.js
+++ b/tests/index.js
@@ -799,6 +799,27 @@ describe('apply function', () => {
             .then(done)
             .catch(done);
         });
+
+        it('transform with promise', (done) => {
+            runEmit({
+                expectedAssetKeys: [
+                    'file.txt'
+                ],
+                expectedAssetContent: {
+                    'file.txt': 'newchanged!'
+                },
+                patterns: [{
+                    from: 'file.txt',
+                    transform: function(content) {
+                        return new Promise((resolve) => {
+                            resolve(content + 'changed!');
+                        });
+                    }
+                }]
+            })
+            .then(done)
+            .catch(done);
+        });
     });
 
     describe('with directory in from', () => {