diff --git a/ChangeLog.txt b/ChangeLog.txt
index 51f94aad1d..3448f9a07d 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -4,6 +4,11 @@
 Broker:
 - Fix bridge not respecting receive-maximum when reconnecting with MQTT v5.
 
+Client library:
+- Fix mosquitto_topic_matches_sub2() not using the length parameters.
+  Closes #2364.
+
+
 2.0.13 - 2021-10-27
 ===================
 
diff --git a/lib/util_topic.c b/lib/util_topic.c
index 62b531127c..e29102f739 100644
--- a/lib/util_topic.c
+++ b/lib/util_topic.c
@@ -189,19 +189,11 @@ int mosquitto_sub_topic_check2(const char *str, size_t len)
 	return MOSQ_ERR_SUCCESS;
 }
 
-int mosquitto_topic_matches_sub(const char *sub, const char *topic, bool *result)
-{
-	return mosquitto_topic_matches_sub2(sub, 0, topic, 0, result);
-}
-
 /* Does a topic match a subscription? */
-int mosquitto_topic_matches_sub2(const char *sub, size_t sublen, const char *topic, size_t topiclen, bool *result)
+int mosquitto_topic_matches_sub(const char *sub, const char *topic, bool *result)
 {
 	size_t spos;
 
-	UNUSED(sublen);
-	UNUSED(topiclen);
-
 	if(!result) return MOSQ_ERR_INVAL;
 	*result = false;
 
@@ -325,3 +317,130 @@ int mosquitto_topic_matches_sub2(const char *sub, size_t sublen, const char *top
 
 	return MOSQ_ERR_SUCCESS;
 }
+
+/* Does a topic match a subscription? */
+int mosquitto_topic_matches_sub2(const char *sub, size_t sublen, const char *topic, size_t topiclen, bool *result)
+{
+	size_t spos, tpos;
+
+	if(!result) return MOSQ_ERR_INVAL;
+	*result = false;
+
+	if(!sub || !topic || !sublen || !topiclen){
+		return MOSQ_ERR_INVAL;
+	}
+
+	if((sub[0] == '$' && topic[0] != '$')
+			|| (topic[0] == '$' && sub[0] != '$')){
+
+		return MOSQ_ERR_SUCCESS;
+	}
+
+	spos = 0;
+	tpos = 0;
+
+	while(spos < sublen){
+		if(tpos < topiclen && (topic[tpos] == '+' || topic[tpos] == '#')){
+			return MOSQ_ERR_INVAL;
+		}
+		if(tpos == topiclen || sub[spos] != topic[tpos]){
+			if(sub[spos] == '+'){
+				/* Check for bad "+foo" or "a/+foo" subscription */
+				if(spos > 0 && sub[spos-1] != '/'){
+					return MOSQ_ERR_INVAL;
+				}
+				/* Check for bad "foo+" or "foo+/a" subscription */
+				if(spos+1 < sublen && sub[spos+1] != '/'){
+					return MOSQ_ERR_INVAL;
+				}
+				spos++;
+				while(tpos < topiclen && topic[tpos] != '/'){
+					if(topic[tpos] == '+' || topic[tpos] == '#'){
+						return MOSQ_ERR_INVAL;
+					}
+					tpos++;
+				}
+				if(tpos == topiclen && spos == sublen){
+					*result = true;
+					return MOSQ_ERR_SUCCESS;
+				}
+			}else if(sub[spos] == '#'){
+				/* Check for bad "foo#" subscription */
+				if(spos > 0 && sub[spos-1] != '/'){
+					return MOSQ_ERR_INVAL;
+				}
+				/* Check for # not the final character of the sub, e.g. "#foo" */
+				if(spos+1 < sublen){
+					return MOSQ_ERR_INVAL;
+				}else{
+					while(tpos < topiclen){
+						if(topic[tpos] == '+' || topic[tpos] == '#'){
+							return MOSQ_ERR_INVAL;
+						}
+						tpos++;
+					}
+					*result = true;
+					return MOSQ_ERR_SUCCESS;
+				}
+			}else{
+				/* Check for e.g. foo/bar matching foo/+/# */
+				if(tpos == topiclen
+						&& spos > 0
+						&& sub[spos-1] == '+'
+						&& sub[spos] == '/'
+						&& spos+1 < sublen
+						&& sub[spos+1] == '#')
+				{
+					*result = true;
+					return MOSQ_ERR_SUCCESS;
+				}
+
+				/* There is no match at this point, but is the sub invalid? */
+				while(spos < sublen){
+					if(sub[spos] == '#' && spos+1 < sublen){
+						return MOSQ_ERR_INVAL;
+					}
+					spos++;
+				}
+
+				/* Valid input, but no match */
+				return MOSQ_ERR_SUCCESS;
+			}
+		}else{
+			/* sub[spos] == topic[tpos] */
+			if(tpos+1 == topiclen){
+				/* Check for e.g. foo matching foo/# */
+				if(spos+3 == sublen
+						&& sub[spos+1] == '/'
+						&& sub[spos+2] == '#'){
+					*result = true;
+					return MOSQ_ERR_SUCCESS;
+				}
+			}
+			spos++;
+			tpos++;
+			if(spos == sublen && tpos == topiclen){
+				*result = true;
+				return MOSQ_ERR_SUCCESS;
+			}else if(tpos == topiclen && sub[spos] == '+' && spos+1 == sublen){
+				if(spos > 0 && sub[spos-1] != '/'){
+					return MOSQ_ERR_INVAL;
+				}
+				spos++;
+				*result = true;
+				return MOSQ_ERR_SUCCESS;
+			}
+		}
+	}
+	if(tpos < topiclen || spos < sublen){
+		*result = false;
+	}
+	while(tpos < topiclen){
+		if(topic[tpos] == '+' || topic[tpos] == '#'){
+			return MOSQ_ERR_INVAL;
+		}
+		tpos++;
+	}
+
+	return MOSQ_ERR_SUCCESS;
+}
diff --git a/test/unit/util_topic_test.c b/test/unit/util_topic_test.c
index b669fcc9c4..df5ee6971d 100644
--- a/test/unit/util_topic_test.c
+++ b/test/unit/util_topic_test.c
@@ -11,6 +11,16 @@ static void match_helper(const char *sub, const char *topic)
 	rc = mosquitto_topic_matches_sub(sub, topic, &match);
 	CU_ASSERT_EQUAL(rc, MOSQ_ERR_SUCCESS);
 	CU_ASSERT_EQUAL(match, true);
+	if(match == false){
+		printf("1: %s:%s\n", sub, topic);
+	}
+
+	rc = mosquitto_topic_matches_sub2(sub, strlen(sub), topic, strlen(topic), &match);
+	CU_ASSERT_EQUAL(rc, MOSQ_ERR_SUCCESS);
+	CU_ASSERT_EQUAL(match, true);
+	if(match == false){
+		printf("2: %s:%s\n", sub, topic);
+	}
 }
 
 static void no_match_helper(int rc_expected, const char *sub, const char *topic)
@@ -24,6 +34,13 @@ static void no_match_helper(int rc_expected, const char *sub, const char *topic)
 		printf("%d:%d %s:%s\n", rc, rc_expected, sub, topic);
 	}
 	CU_ASSERT_EQUAL(match, false);
+
+	rc = mosquitto_topic_matches_sub2(sub, strlen(sub), topic, strlen(topic), &match);
+	CU_ASSERT_EQUAL(rc, rc_expected);
+	if(rc != rc_expected){
+		printf("%d:%d %s:%s\n", rc, rc_expected, sub, topic);
+	}
+	CU_ASSERT_EQUAL(match, false);
 }
 
 /* ========================================================================