diff --git a/app/assets/javascripts/diffs/store/mutation_types.js b/app/assets/javascripts/diffs/store/mutation_types.js
index 4436935c1ec291c0c0208805fcd774cdbb933aaa..699c61b3ddda220817dd0a92a43a31db3a2783ea 100644
--- a/app/assets/javascripts/diffs/store/mutation_types.js
+++ b/app/assets/javascripts/diffs/store/mutation_types.js
@@ -2,8 +2,11 @@ export const SET_BASE_CONFIG = 'SET_BASE_CONFIG';
 export const SET_LOADING = 'SET_LOADING';
 export const SET_BATCH_LOADING = 'SET_BATCH_LOADING';
 export const SET_RETRIEVING_BATCHES = 'SET_RETRIEVING_BATCHES';
+
 export const SET_DIFF_DATA = 'SET_DIFF_DATA';
 export const SET_DIFF_DATA_BATCH = 'SET_DIFF_DATA_BATCH';
+export const SET_DIFF_FILES = 'SET_DIFF_FILES';
+
 export const SET_DIFF_VIEW_TYPE = 'SET_DIFF_VIEW_TYPE';
 export const SET_COVERAGE_DATA = 'SET_COVERAGE_DATA';
 export const SET_MERGE_REQUEST_DIFFS = 'SET_MERGE_REQUEST_DIFFS';
diff --git a/app/assets/javascripts/diffs/store/mutations.js b/app/assets/javascripts/diffs/store/mutations.js
index bb4c80b5759829dbe0e5dc474d60441a19c62b68..3c00ae98e7517b5009f74574d97a7271742ac765 100644
--- a/app/assets/javascripts/diffs/store/mutations.js
+++ b/app/assets/javascripts/diffs/store/mutations.js
@@ -10,6 +10,10 @@ import {
 } from './utils';
 import * as types from './mutation_types';
 
+function updateDiffFilesInState(state, files) {
+  return Object.assign(state, { diffFiles: files });
+}
+
 export default {
   [types.SET_BASE_CONFIG](state, options) {
     const {
@@ -46,6 +50,10 @@ export default {
     Object.assign(state, { retrievingBatches });
   },
 
+  [types.SET_DIFF_FILES](state, files) {
+    updateDiffFilesInState(state, files);
+  },
+
   [types.SET_DIFF_DATA](state, data) {
     let files = state.diffFiles;
 
@@ -58,8 +66,8 @@ export default {
 
     Object.assign(state, {
       ...convertObjectPropsToCamelCase(data),
-      diffFiles: files,
     });
+    updateDiffFilesInState(state, files);
   },
 
   [types.SET_DIFF_DATA_BATCH](state, data) {
@@ -67,8 +75,8 @@ export default {
 
     Object.assign(state, {
       ...convertObjectPropsToCamelCase(data),
-      diffFiles: files,
     });
+    updateDiffFilesInState(state, files);
   },
 
   [types.SET_COVERAGE_DATA](state, coverageFiles) {
diff --git a/spec/frontend/diffs/store/mutations_spec.js b/spec/frontend/diffs/store/mutations_spec.js
index f486a53fc4d4bc846a5cac010d3077e1c8e5c78a..ad05f27b3259d7e79f5528b6a242f47ea293a304 100644
--- a/spec/frontend/diffs/store/mutations_spec.js
+++ b/spec/frontend/diffs/store/mutations_spec.js
@@ -51,6 +51,24 @@ describe('DiffsStoreMutations', () => {
     });
   });
 
+  describe('SET_DIFF_FILES', () => {
+    it('should set diffFiles in state', () => {
+      const state = {};
+
+      mutations[types.SET_DIFF_FILES](state, ['file', 'another file']);
+
+      expect(state.diffFiles.length).toEqual(2);
+    });
+
+    it('should not set anything except diffFiles in state', () => {
+      const state = {};
+
+      mutations[types.SET_DIFF_FILES](state, ['file', 'another file']);
+
+      expect(Object.keys(state)).toEqual(['diffFiles']);
+    });
+  });
+
   describe('SET_DIFF_DATA', () => {
     it('should set diff data type properly', () => {
       const state = {