diff --git a/lib/property-types.js b/lib/property-types.js
index f9479ae..c1e62a5 100644
--- a/lib/property-types.js
+++ b/lib/property-types.js
@@ -1,14 +1,14 @@
 module.exports = {
-  String: {
+  string: {
     defaultName: 'string'
   },
-  Number: {
+  number: {
     defaultName: 'number'
   },
-  Boolean: {
+  boolean: {
     defaultName: 'boolean'
   },
-  Date: {
+  date: {
     defaultName: 'date'
   }
 };
\ No newline at end of file