diff --git a/src/mqtt/qmqttcontrolpacket.cpp b/src/mqtt/qmqttcontrolpacket.cpp
index 7b1a637..0c4a968 100644
--- a/src/mqtt/qmqttcontrolpacket.cpp
+++ b/src/mqtt/qmqttcontrolpacket.cpp
@@ -56,7 +56,10 @@ void QMqttControlPacket::clear()
 
 void QMqttControlPacket::setHeader(quint8 h)
 {
-    m_header = h;
+    if (h < QMqttControlPacket::CONNECT || h > DISCONNECT || h & 0x0F)
+        m_header = QMqttControlPacket::UNKNOWN;
+    else
+        m_header = h;
 }
 
 void QMqttControlPacket::append(char value)
diff --git a/src/mqtt/qmqttcontrolpacket_p.h b/src/mqtt/qmqttcontrolpacket_p.h
index fae6710..ecee854 100644
--- a/src/mqtt/qmqttcontrolpacket_p.h
+++ b/src/mqtt/qmqttcontrolpacket_p.h
@@ -50,6 +50,7 @@ class Q_AUTOTEST_EXPORT QMqttControlPacket
 {
 public:
     enum PacketType {
+        UNKNOWN     = 0x00,
         CONNECT     = 0x10,
         CONNACK     = 0x20,
         PUBLISH     = 0x30,
@@ -63,7 +64,7 @@ public:
         UNSUBACK    = 0xB0,
         PINGREQ     = 0xC0,
         PINGRESP    = 0xD0,
-        DISCONNECT  = 0xE0
+        DISCONNECT  = 0xE0,
     };
 
     QMqttControlPacket();
@@ -82,7 +83,7 @@ public:
     QByteArray serialize() const;
     inline QByteArray payload() const { return m_payload; }
 private:
-    quint8 m_header;
+    quint8 m_header{UNKNOWN};
     QByteArray m_payload;
 };
 
diff --git a/tests/auto/qmqttcontrolpacket/qmqttcontrolpacket/tst_qmqttcontrolpacket.cpp b/tests/auto/qmqttcontrolpacket/qmqttcontrolpacket/tst_qmqttcontrolpacket.cpp
index 20c940c..1c128b9 100644
--- a/tests/auto/qmqttcontrolpacket/qmqttcontrolpacket/tst_qmqttcontrolpacket.cpp
+++ b/tests/auto/qmqttcontrolpacket/qmqttcontrolpacket/tst_qmqttcontrolpacket.cpp
@@ -44,6 +44,9 @@ void Tst_QMqttControlPacket::header()
 
         packet.clear();
         QVERIFY(packet.header() == QMqttControlPacket::UNKNOWN);
+
+        packet.setHeader(42);
+        QVERIFY(packet.header() == QMqttControlPacket::UNKNOWN);
     }
 }