diff --git a/lib/util_topic.c b/lib/util_topic.c
index 45a2d311..18fbceb1 100644
--- a/lib/util_topic.c
+++ b/lib/util_topic.c
@@ -179,7 +179,7 @@ int mosquitto_topic_matches_sub2(const char *sub, size_t sublen, const char *top
 		if(topic[tpos] == '+' || topic[tpos] == '#'){
 			return MOSQ_ERR_INVAL;
 		}
-		if(sub[spos] != topic[tpos]){
+		if(tpos == topiclen || sub[spos] != topic[tpos]){ /* Check for wildcard matches */
 			if(sub[spos] == '+'){
 				/* Check for bad "+foo" or "a/+foo" subscription */
 				if(spos > 0 && sub[spos-1] != '/'){
@@ -198,10 +198,11 @@ int mosquitto_topic_matches_sub2(const char *sub, size_t sublen, const char *top
 					return MOSQ_ERR_SUCCESS;
 				}
 			}else if(sub[spos] == '#'){
+				/* Check for bad "foo#" subscription */
 				if(spos > 0 && sub[spos-1] != '/'){
 					return MOSQ_ERR_INVAL;
 				}
-				multilevel_wildcard = true;
+				/* Check for # not the final character of the sub, e.g. "#foo" */
 				if(spos+1 != sublen){
 					return MOSQ_ERR_INVAL;
 				}else{
@@ -221,9 +222,19 @@ int mosquitto_topic_matches_sub2(const char *sub, size_t sublen, const char *top
 					multilevel_wildcard = true;
 					return MOSQ_ERR_SUCCESS;
 				}
+
+				/* There is no match at this point, but is the sub invalid? */
+				for(int i=spos; i<sublen; i++){
+					if(sub[i] == '#' && i+1 != sublen){
+						return MOSQ_ERR_INVAL;
+					}
+				}
+
+				/* Valid input, but no match */
 				return MOSQ_ERR_SUCCESS;
 			}
 		}else{
+			/* sub[spos] == topic[tpos] */
 			if(tpos == topiclen-1){
 				/* Check for e.g. foo matching foo/# */
 				if(spos == sublen-3
diff --git a/test/unit/util_topic_test.c b/test/unit/util_topic_test.c
index 39900826..88f668a2 100644
--- a/test/unit/util_topic_test.c
+++ b/test/unit/util_topic_test.c
@@ -149,7 +149,6 @@ static void TEST_valid_no_matching(void)
 	no_match_helper(MOSQ_ERR_SUCCESS, "foo/+/#", "fo2/bar/baz");
 
 	no_match_helper(MOSQ_ERR_SUCCESS, "/#", "foo/bar");
-	no_match_helper(MOSQ_ERR_SUCCESS, "/#a", "foo/bar");
 
 	no_match_helper(MOSQ_ERR_SUCCESS, "#", "$SYS/bar");
 	no_match_helper(MOSQ_ERR_SUCCESS, "$BOB/bar", "$SYS/bar");
@@ -162,6 +161,11 @@ static void TEST_invalid(void)
 	no_match_helper(MOSQ_ERR_INVAL, "fo#o/", "foo");
 	no_match_helper(MOSQ_ERR_INVAL, "foo#", "fooa");
 	no_match_helper(MOSQ_ERR_INVAL, "foo+", "foo");
+	no_match_helper(MOSQ_ERR_INVAL, "foo/#a", "foo");
+	no_match_helper(MOSQ_ERR_INVAL, "#a", "foo");
+	no_match_helper(MOSQ_ERR_INVAL, "foo/#abc", "foo");
+	no_match_helper(MOSQ_ERR_INVAL, "#abc", "foo");
+	no_match_helper(MOSQ_ERR_INVAL, "/#a", "foo/bar");
 }
 
 /* ========================================================================