diff --git a/src/util/ColorMixin.js b/src/util/ColorMixin.js
index 59a31ca..2379bae 100644
--- a/src/util/ColorMixin.js
+++ b/src/util/ColorMixin.js
@@ -8,7 +8,7 @@
  */
 
 
-import {Color} from './Color';
+import {Color} from './Color.js';
 
 
 /**
diff --git a/src/util/EventEmitter.js b/src/util/EventEmitter.js
index 5f4ad88..3f5814a 100644
--- a/src/util/EventEmitter.js
+++ b/src/util/EventEmitter.js
@@ -8,7 +8,7 @@
  */
 
 
-import * as util from './Util';
+import * as util from './Util.js';
 
 
 /**
diff --git a/src/util/PsychObject.js b/src/util/PsychObject.js
index 381a6f9..fe955bd 100644
--- a/src/util/PsychObject.js
+++ b/src/util/PsychObject.js
@@ -9,8 +9,8 @@
  */
 
 
-import {EventEmitter} from './EventEmitter';
-import * as util from './Util';
+import {EventEmitter} from './EventEmitter.js';
+import * as util from './Util.js';
 
 
 /**