diff --git a/_parser.py b/_parser.py
index 83aab38..6466124 100644
--- a/_parser.py
+++ b/_parser.py
@@ -25,7 +25,7 @@
 
     b_clause = "B)" _ datetime
     c_clause = "C)" _ ((datetime estimated?) / permanent)
-    estimated = "EST"
+    estimated = _? "EST"
     permanent = "PERM"
 
     d_clause = "D)" _ till_next_clause
@@ -174,4 +174,4 @@ def generic_visit(self, _, visited_children):
         return visited_children
 
     def visit_root(self, node, _):
-        self.tgt.full_text = node.full_text
\ No newline at end of file
+        self.tgt.full_text = node.full_text