diff --git a/README.md b/README.md
index 0145ed99..06a8d27b 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 Build a Molecule
 ================
 
-"Build a Molecule" is an educational simulation in HTML5, by <a href="http://phet.colorado.edu/" target="_blank">PhET Interactive Simulations</a>
+"Build a Molecule" is an educational simulation in HTML5, by <a href="https://phet.colorado.edu/" target="_blank">PhET Interactive Simulations</a>
 at the University of Colorado Boulder.
 
 *This simulation is under development and has not been published.*