diff --git a/lib/controllers/git-controller.js b/lib/controllers/git-controller.js
index 3034b5cd5f..415b8fc558 100644
--- a/lib/controllers/git-controller.js
+++ b/lib/controllers/git-controller.js
@@ -209,7 +209,8 @@ export default class GitController extends React.Component {
     const repository = this.props.repository;
     if (!repository) { return null; }
 
-    const filePatch = await repository.getFilePatchForPath(filePath, {staged: stagingStatus === 'staged', amending});
+    const staged = stagingStatus === 'staged';
+    const filePatch = await repository.getFilePatchForPath(filePath, {staged, amending: staged && amending});
     return new Promise(resolve => {
       if (filePatch) {
         this.setState({filePath, filePatch, stagingStatus}, () => {
diff --git a/test/controllers/git-controller.test.js b/test/controllers/git-controller.test.js
index ab7e28b7fb..d7fcf04881 100644
--- a/test/controllers/git-controller.test.js
+++ b/test/controllers/git-controller.test.js
@@ -188,6 +188,20 @@ describe('GitController', function() {
         assert.notEqual(originalFilePatch, wrapper.state('filePatch'));
       });
     });
+
+    // https://github.com/atom/github/issues/505
+    it('calls repository.getFilePatchForPath with amending: true only if staging status is staged', async () => {
+      const workdirPath = await cloneRepository('three-files');
+      const repository = await buildRepository(workdirPath);
+
+      app = React.cloneElement(app, {repository});
+      const wrapper = shallow(app);
+
+      sinon.stub(repository, 'getFilePatchForPath');
+      await wrapper.instance().showFilePatchForPath('a.txt', 'unstaged', {amending: true});
+      assert.equal(repository.getFilePatchForPath.callCount, 1);
+      assert.deepEqual(repository.getFilePatchForPath.args[0], ['a.txt', {staged: false, amending: false}]);
+    });
   });
 
   describe('diveIntoFilePatchForPath(filePath, staged, {amending, activate})', function() {