diff --git a/public/js/debug-console.js b/public/js/debug-console.js
index 8b01de4..18ef319 100644
--- a/public/js/debug-console.js
+++ b/public/js/debug-console.js
@@ -8,7 +8,12 @@
     window.console[func] = function(msg) {
       var style = null;
       var messages = Array.prototype.slice.call(arguments);
-      if (arguments[0].indexOf('%c') > -1 && arguments.length > 1) {
+
+      // e.g. console.log('%cHello', 'background: red', 'foobar');
+      if (arguments.length > 1 &&
+          typeof arguments[0] === 'string' &&
+          typeof arguments[1] === 'string' &&
+          arguments[0].indexOf('%c') > -1) {
         style = arguments[1];
         messages.splice(1, 1); // remove style string from console output
       }