diff --git a/src/lib/custom-style.html b/src/lib/custom-style.html
index a2d2ef680d..1a9a338b4c 100644
--- a/src/lib/custom-style.html
+++ b/src/lib/custom-style.html
@@ -81,7 +81,8 @@
     extends: 'style',
 
     properties: {
-      module: {}
+      // module is a property so that it deserializes
+      module: String
     },
 
     ready: function() {