diff --git a/csventry.py b/csventry.py
index c6cba52..53562f0 100644
--- a/csventry.py
+++ b/csventry.py
@@ -1,10 +1,31 @@
 import csv
 
+class CSVFieldUnknown(Exception):
+    def __init__(self, cls, field):
+        super(CSVFieldUnknown, self).__init__(
+            "Unknown field %s for class %s" % (
+                field,
+                cls.__name__
+            )
+        )
+
 class CSVEntry:
+    _contents = {}
     def __init__(self, **kvargs):
-        assert ( set(kvargs.keys()) - set(self.__class__.fields) ) == set()
         for field in self.__class__.fields:
-            setattr(self, field, kvargs[field] or "")
+            setattr(self, field, "")
+        for field, val in kvargs.items():
+            setattr(self, field, val)
+
+    def __getattr__(self, key):
+        if key not in self.__class__.fields:
+            raise CSVFieldUnknown(self.__class__, key)
+        return self._contents[key]
+
+    def __setattr__(self, key, value):
+        if key not in self.__class__.fields:
+            raise CSVFieldUnknown(self.__class__, key)
+        self._contents[key] = value
 
     @classmethod
     def fromRow(cls, row):