diff --git a/ChangeLog.txt b/ChangeLog.txt
index 02312884..419b2d4e 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -6,6 +6,7 @@
   of that client. Closes #3487.
 - Fix password length not being passed to MOSQ_EVT_BASIC_AUTH events.
   Closes #3490.
+- Fix incorrect maximum-packet-size restriction. Closes #3503.
 
 # Common lib:
 - Fix potential crash if reading a file in restricted mode and the group id
diff --git a/lib/packet_mosq.c b/lib/packet_mosq.c
index d1379d3d..48b0efbd 100644
--- a/lib/packet_mosq.c
+++ b/lib/packet_mosq.c
@@ -238,7 +238,7 @@ int packet__check_oversize(struct mosquitto *mosq, uint32_t remaining_length)
 		return MOSQ_ERR_SUCCESS;
 	}
 
-	len = remaining_length + mosquitto_varint_bytes(remaining_length);
+	len = 1 + remaining_length + mosquitto_varint_bytes(remaining_length);
 	if(len > mosq->maximum_packet_size){
 		return MOSQ_ERR_OVERSIZE_PACKET;
 	}else{
diff --git a/test/broker/12-prop-maximum-packet-size-publish-qos1.py b/test/broker/12-prop-maximum-packet-size-publish-qos1.py
index 2900c3c7..2530a377 100755
--- a/test/broker/12-prop-maximum-packet-size-publish-qos1.py
+++ b/test/broker/12-prop-maximum-packet-size-publish-qos1.py
@@ -17,13 +17,18 @@ def do_test(start_broker):
     suback_packet = mosq_test.gen_suback(mid, 1, proto_ver=5)
 
     mid=1
-    publish1_packet = mosq_test.gen_publish(topic="12/max/publish/qos1/test/topic", mid=mid, qos=1, payload="12345678901234567890", proto_ver=5)
+    publish1_packet = mosq_test.gen_publish(topic="12/max/publish/qos1/test/topic", mid=mid, qos=1, payload="1234", proto_ver=5)
     puback1_packet = mosq_test.gen_puback(mid, proto_ver=5)
 
     mid=2
-    publish2_packet = mosq_test.gen_publish(topic="12/max/publish/qos1/test/topic", mid=mid, qos=1, payload="7890", proto_ver=5)
+    props = mqtt5_props.gen_byte_prop(mqtt5_props.PAYLOAD_FORMAT_INDICATOR, 1)
+    publish2_packet = mosq_test.gen_publish(topic="12/max/publish/qos1/test/topic", mid=mid, qos=1, payload="56", proto_ver=5, properties=props)
     puback2_packet = mosq_test.gen_puback(mid, proto_ver=5)
 
+    mid=3
+    publish3_packet = mosq_test.gen_publish(topic="12/max/publish/qos1/test/topic", mid=mid, qos=1, payload="789", proto_ver=5)
+    puback3_packet = mosq_test.gen_puback(mid, proto_ver=5)
+
     port = mosq_test.get_port()
     if start_broker:
         broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port)
@@ -33,12 +38,15 @@ def do_test(start_broker):
         mosq_test.do_send_receive(sock, subscribe_packet, suback_packet)
 
         mosq_test.do_send_receive(sock, publish1_packet, puback1_packet, "puback 1")
-
         # We shouldn't receive the publish here because it is > MAXIMUM_PACKET_SIZE
         mosq_test.do_ping(sock)
 
-        sock.send(publish2_packet)
-        mosq_test.receive_unordered(sock, puback2_packet, publish2_packet, "puback 2/publish2")
+        mosq_test.do_send_receive(sock, publish2_packet, puback2_packet, "puback 2")
+        # We shouldn't receive the publish here because it is > MAXIMUM_PACKET_SIZE
+        mosq_test.do_ping(sock)
+
+        sock.send(publish3_packet)
+        mosq_test.receive_unordered(sock, puback3_packet, publish3_packet, "puback 3/publish3")
         rc = 0
     except mosq_test.TestError:
         pass
diff --git a/test/broker/12-prop-maximum-packet-size-publish-qos2.py b/test/broker/12-prop-maximum-packet-size-publish-qos2.py
index e0ad9343..7256d254 100755
--- a/test/broker/12-prop-maximum-packet-size-publish-qos2.py
+++ b/test/broker/12-prop-maximum-packet-size-publish-qos2.py
@@ -17,13 +17,13 @@ def do_test(start_broker):
     suback_packet = mosq_test.gen_suback(mid, 2, proto_ver=5)
 
     mid=1
-    publish1_packet = mosq_test.gen_publish(topic="12/max/publish/qos2/test/topic", mid=mid, qos=2, payload="12345678901234567890", proto_ver=5)
+    publish1_packet = mosq_test.gen_publish(topic="12/max/publish/qos2/test/topic", mid=mid, qos=2, payload="1234", proto_ver=5)
     pubrec1_packet = mosq_test.gen_pubrec(mid, proto_ver=5)
     pubrel1_packet = mosq_test.gen_pubrel(mid, proto_ver=5)
     pubcomp1_packet = mosq_test.gen_pubcomp(mid, proto_ver=5)
 
     mid=2
-    publish2_packet = mosq_test.gen_publish(topic="12/max/publish/qos2/test/topic", mid=mid, qos=2, payload="7890", proto_ver=5)
+    publish2_packet = mosq_test.gen_publish(topic="12/max/publish/qos2/test/topic", mid=mid, qos=2, payload="789", proto_ver=5)
     pubrec2_packet = mosq_test.gen_pubrec(mid, proto_ver=5)
     pubrel2_packet = mosq_test.gen_pubrel(mid, proto_ver=5)
     pubcomp2_packet = mosq_test.gen_pubcomp(mid, proto_ver=5)
diff --git a/test/lib/11-prop-oversize-packet.py b/test/lib/11-prop-oversize-packet.py
index f8f56697..e537eef3 100755
--- a/test/lib/11-prop-oversize-packet.py
+++ b/test/lib/11-prop-oversize-packet.py
@@ -13,8 +13,8 @@ def do_test(conn, data):
     props += mqtt5_props.gen_uint16_prop(mqtt5_props.RECEIVE_MAXIMUM, 20)
     connack_packet = mosq_test.gen_connack(rc=0, proto_ver=5, properties=props, property_helper=False)
 
-    bad_publish_packet = mosq_test.gen_publish("pub/test", qos=0, payload="0123456789012345678", proto_ver=5)
-    publish_packet = mosq_test.gen_publish("pub/test", qos=0, payload="012345678901234567", proto_ver=5)
+    bad_publish_packet = mosq_test.gen_publish("pub/test", qos=0, payload="123456789012345678", proto_ver=5)
+    publish_packet = mosq_test.gen_publish("pub/test", qos=0, payload="12345678901234567", proto_ver=5)
 
     disconnect_packet = mosq_test.gen_disconnect()
 
diff --git a/test/lib/c/11-prop-oversize-packet.c b/test/lib/c/11-prop-oversize-packet.c
index 6f9624a8..a857e936 100644
--- a/test/lib/c/11-prop-oversize-packet.c
+++ b/test/lib/c/11-prop-oversize-packet.c
@@ -27,12 +27,12 @@ static void on_connect(struct mosquitto *mosq, void *obj, int rc)
 			exit(1);
 		}
 
-		rc = mosquitto_publish(mosq, &sent_mid, "pub/test", strlen("0123456789012345678"), "0123456789012345678", 0, false);
+		rc = mosquitto_publish(mosq, &sent_mid, "pub/test", strlen("123456789012345678"), "123456789012345678", 0, false);
 		if(rc != MOSQ_ERR_OVERSIZE_PACKET){
 			printf("Fail on publish 1\n");
 			exit(1);
 		}
-		rc = mosquitto_publish(mosq, &sent_mid, "pub/test", strlen("012345678901234567"), "012345678901234567", 0, false);
+		rc = mosquitto_publish(mosq, &sent_mid, "pub/test", strlen("12345678901234567"), "12345678901234567", 0, false);
 		if(rc != MOSQ_ERR_SUCCESS){
 			printf("Fail on publish 2\n");
 			exit(1);
diff --git a/test/lib/cpp/11-prop-oversize-packet.cpp b/test/lib/cpp/11-prop-oversize-packet.cpp
index 880df48e..abd76186 100644
--- a/test/lib/cpp/11-prop-oversize-packet.cpp
+++ b/test/lib/cpp/11-prop-oversize-packet.cpp
@@ -36,12 +36,12 @@ void mosquittopp_test::on_connect(int rc)
 			exit(1);
 		}
 
-		rc = publish(&sent_mid, "pub/test", strlen("0123456789012345678"), "0123456789012345678", 0, false);
+		rc = publish(&sent_mid, "pub/test", strlen("123456789012345678"), "123456789012345678", 0, false);
 		if(rc != MOSQ_ERR_OVERSIZE_PACKET){
 			printf("Fail on publish 1\n");
 			exit(1);
 		}
-		rc = publish(&sent_mid, "pub/test", strlen("012345678901234567"), "012345678901234567", 0, false);
+		rc = publish(&sent_mid, "pub/test", strlen("12345678901234567"), "12345678901234567", 0, false);
 		if(rc != MOSQ_ERR_SUCCESS){
 			printf("Fail on publish 2\n");
 			exit(1);