diff --git a/bifromq-util/src/main/java/org/apache/bifromq/util/TopicUtil.java b/bifromq-util/src/main/java/org/apache/bifromq/util/TopicUtil.java
index 73288fd49..21f3e0028 100644
--- a/bifromq-util/src/main/java/org/apache/bifromq/util/TopicUtil.java
+++ b/bifromq-util/src/main/java/org/apache/bifromq/util/TopicUtil.java
@@ -110,6 +110,9 @@ public static boolean isValidTopicFilter(String topicFilter, int maxLevelLength,
             topicLevelLength = 0;
             // skip one separator to real topicFilter start pos
             i++;
+            if (i >= topicFilter.length()) {
+                return false;
+            }
         }
         int startIdx = i;
         int level = 1;
diff --git a/bifromq-util/src/test/java/org/apache/bifromq/util/TopicUtilsTest.java b/bifromq-util/src/test/java/org/apache/bifromq/util/TopicUtilsTest.java
index 25b096a83..2ea138fa2 100644
--- a/bifromq-util/src/test/java/org/apache/bifromq/util/TopicUtilsTest.java
+++ b/bifromq-util/src/test/java/org/apache/bifromq/util/TopicUtilsTest.java
@@ -132,7 +132,7 @@ public void testIsValidTopicFilter() {
         assertTrue(TopicUtil.isValidTopicFilter("$oshare", 10, 4, 100));
         assertTrue(TopicUtil.isValidTopicFilter("$shared/", 10, 4, 10));
         assertTrue(TopicUtil.isValidTopicFilter("$oshared/", 10, 4, 100));
-        assertTrue(TopicUtil.isValidTopicFilter("$share/g/", 10, 4, 100));
+        assertFalse(TopicUtil.isValidTopicFilter("$share/g/", 10, 4, 100));
         assertTrue(TopicUtil.isValidTopicFilter("$share/g//", 10, 4, 100));
         assertFalse(TopicUtil.isValidTopicFilter("$share/g/abcdef/", 5, 4, 10));
         assertFalse(TopicUtil.isValidTopicFilter("$share/g/1/2/3/4/5", 5, 4, 255));