diff --git a/lib/util.js b/lib/util.js
index 43d954c..212c1e2 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -30,6 +30,9 @@ module.exports = {
   decorateRouteWithPrerequisites (app, route) {
     const policies = app.config.policies
     const prerequisites = lib.Util.getRoutePrerequisites(policies, route)
+    if (!_.isArray(prerequisites)) {
+      throw new TypeError(['trailpack-router: policy', prerequisites, 'must be an array.'].join(' '))
+    }
 
     return _.defaultsDeep({ }, route, {
       config: {