diff --git a/lib/spawn-command.js b/lib/spawn-command.js
index 3bd29bec..83960f0c 100644
--- a/lib/spawn-command.js
+++ b/lib/spawn-command.js
@@ -15,7 +15,7 @@ const spawnCommand = module.exports;
  * @param {object} [opt] any execa options
  * @return {String} spawned process reference
  */
-spawnCommand.spawnCommand = (command, args, opt) => {
+spawnCommand.spawnCommand = function (command, args, opt) {
   return spawn(command, args, {stdio: 'inherit', cwd: this.cwd, ...opt});
 };
 
@@ -27,6 +27,6 @@ spawnCommand.spawnCommand = (command, args, opt) => {
  * @param {object} [opt] any execa options
  * @return {String} spawn.sync result
  */
-spawnCommand.spawnCommandSync = (command, args, opt) => {
+spawnCommand.spawnCommandSync = function (command, args, opt) {
   return spawn.sync(command, args, {stdio: 'inherit', cwd: this.cwd, ...opt});
 };
diff --git a/test/spawn-command.js b/test/spawn-command.js
index 784df06b..e55cf771 100644
--- a/test/spawn-command.js
+++ b/test/spawn-command.js
@@ -8,9 +8,10 @@ describe('environment (spawn-command)', () => {
   beforeEach(function () {
     this.spawnLib = sinon.stub();
     this.spawnLib.sync = sinon.stub();
-    this.spawn = proxyquire('../lib/spawn-command', {
+    this.spawn = {};
+    Object.assign(this.spawn, proxyquire('../lib/spawn-command', {
       execa: this.spawnLib
-    });
+    }));
     cwd = Math.random().toString(36).slice(7);
     this.spawn.cwd = cwd;
   });