diff --git a/index.html b/index.html
index 6af141d..0d73391 100644
--- a/index.html
+++ b/index.html
@@ -287,7 +287,7 @@ <h3>GitHub</h3>
 
 <script src="lib/seedrandom.js"></script>
 <script src="lib/box2d.js"></script>
-<script src="http://d3js.org/d3.v3.min.js"></script>
+<script src="https://d3js.org/d3.v3.min.js"></script>
 <script src="https://cdnjs.cloudflare.com/ajax/libs/vis/4.20.0/vis.min.js" ></script>
 <script src="bundle.js"></script>