diff --git a/app/Umbraco/Umbraco.Archetype/PropertyConverters/ArchetypeValueConverter.cs b/app/Umbraco/Umbraco.Archetype/PropertyConverters/ArchetypeValueConverter.cs
index 2834b36..f38a029 100644
--- a/app/Umbraco/Umbraco.Archetype/PropertyConverters/ArchetypeValueConverter.cs
+++ b/app/Umbraco/Umbraco.Archetype/PropertyConverters/ArchetypeValueConverter.cs
@@ -39,8 +39,9 @@ namespace Archetype.Umbraco.PropertyConverters
             if (!sourceString.DetectIsJson())
                 return defaultValue;
 
-            var archetype = new ArchetypeHelper().DeserializeJsonToArchetype(source.ToString(), propertyType.DataTypeId);
-
+            var archetype = new ArchetypeHelper().DeserializeJsonToArchetype(source.ToString(),
+                (propertyType != null ? propertyType.DataTypeId : -1));
+
             return archetype;
         }