diff --git a/src/main/java/com/worksap/nlp/lucene/sudachi/ja/PartOfSpeechTrie.java b/src/main/java/com/worksap/nlp/lucene/sudachi/ja/PartOfSpeechTrie.java
index a8e8fb21..e50d9e7d 100644
--- a/src/main/java/com/worksap/nlp/lucene/sudachi/ja/PartOfSpeechTrie.java
+++ b/src/main/java/com/worksap/nlp/lucene/sudachi/ja/PartOfSpeechTrie.java
@@ -23,6 +23,7 @@
 public class PartOfSpeechTrie {
 
     static final String EMPTY_SYMBOL = "*";
+    static final String LEAF = "";
 
     Map<String, Object> root = new HashMap<>();
 
@@ -37,6 +38,7 @@ public void add(String... items) {
                 (Map<String, Object>)node.computeIfAbsent(item, k -> new HashMap<>());
             node = newNode;
         }
+        node.put(LEAF, LEAF);
     }
 
     public boolean isPrefixOf(List<String> items, int begin, int end) {
@@ -47,17 +49,17 @@ public boolean isPrefixOf(List<String> items, int begin, int end) {
         for (int i = begin; i < end; i++) {
             String item = items.get(i);
             if (EMPTY_SYMBOL.equals(item)) {
-                return node.isEmpty();
+                return node.containsKey(LEAF);
             }
             @SuppressWarnings("unchecked")
             Map<String, Object> newNode = (Map<String, Object>)node.get(item);
             node = newNode;
             if (node == null) {
                 return false;
-            } else if (node.isEmpty()) {
+            } else if (node.containsKey(LEAF)) {
                 return true;
             }
         }
-        return true;
+        return node.containsKey(LEAF);
     }
 }
diff --git a/src/test/java/com/worksap/nlp/lucene/sudachi/ja/TestSudachiPartOfSpeechStopFilter.java b/src/test/java/com/worksap/nlp/lucene/sudachi/ja/TestSudachiPartOfSpeechStopFilter.java
index d816517b..0728b136 100644
--- a/src/test/java/com/worksap/nlp/lucene/sudachi/ja/TestSudachiPartOfSpeechStopFilter.java
+++ b/src/test/java/com/worksap/nlp/lucene/sudachi/ja/TestSudachiPartOfSpeechStopFilter.java
@@ -91,4 +91,21 @@ public void testConjugationForm() throws IOException {
         assertTokenStreamContents(tokenStream,
                                   new String[] {"東京都", "東京", "都", "に", "行っ"});
     }
+
+    public void testPrefixWithUnmatchedSubcategory() throws IOException {
+        String tags = "助詞,格助詞\n助詞,格助詞,引用\n";
+        factory.inform(new StringResourceLoader(tags));
+        tokenStream = factory.create(tokenStream);
+        assertTokenStreamContents(tokenStream,
+                                  new String[] {"東京都", "東京", "都", "行っ", "た"});
+    }
+
+    public void testTooLongCategory() throws IOException {
+        String tags = "名詞,固有名詞,地名,一般,一般\n";
+        factory.inform(new StringResourceLoader(tags));
+        tokenStream = factory.create(tokenStream);
+        assertTokenStreamContents(tokenStream,
+                                  new String[] {"東京都", "東京", "都", "に", "行っ", "た"});
+    }
+
 }