diff --git a/uttut/pipeline/ops/utils/trie.py b/uttut/pipeline/ops/utils/trie.py
index ca849d5..f80ea55 100644
--- a/uttut/pipeline/ops/utils/trie.py
+++ b/uttut/pipeline/ops/utils/trie.py
@@ -5,9 +5,7 @@ def __init__(self):
         self._word = None
 
     def has_child(self, key):
-        if key in self._children:
-            return True
-        return False
+        return key in self._children
 
     def get_child(self, key):
         return self._children[key]
@@ -16,7 +14,10 @@ def insert_child(self, key):
         self._children[key] = TrieNode()
 
     def set_word(self, word):
-        self._word = word
+        if not self._word:
+            self._word = word
+        else:
+            raise ValueError('Word exists')
 
     def get_word(self):
         return self._word