diff --git a/Interpreter.cs b/Interpreter.cs
index 45aeee7..e1bad2e 100644
--- a/Interpreter.cs
+++ b/Interpreter.cs
@@ -508,10 +508,10 @@ public class Interpreter : AST.IExprVisitor<Env, object>
 					throw new RuntimeError(tok, "Record updates must be to unique fields.");
 				}
 				updateLabels.Add(label);
-				if (update.Value == null) throw new NotImplementedException();
+				var updateValue = update.Value == null ? env[update.Name] : evaluate(env, update.Value);
 				try
 				{
-					baseRec = baseRec.Update(label, evaluate(env, update.Value));
+					baseRec = baseRec.Update(label, updateValue);
 				}
 				catch
 				{