diff --git a/broker/src/main/java/io/moquette/broker/Session.java b/broker/src/main/java/io/moquette/broker/Session.java
index 226c12a1f..f41fecd5e 100644
--- a/broker/src/main/java/io/moquette/broker/Session.java
+++ b/broker/src/main/java/io/moquette/broker/Session.java
@@ -299,17 +299,19 @@ public void resendInflightNotAcked() {
         debugLogPacketIds(expired);
 
         for (InFlightPacket notAckPacketId : expired) {
-            if (inflightWindow.containsKey(notAckPacketId.packetId)) {
-                final SessionRegistry.PublishedMessage msg =
-                    (SessionRegistry.PublishedMessage) inflightWindow.get(notAckPacketId.packetId);
-                final Topic topic = msg.topic;
-                final MqttQoS qos = msg.publishingQos;
-                final ByteBuf payload = msg.payload;
-                final ByteBuf copiedPayload = payload.retainedDuplicate();
-                MqttPublishMessage publishMsg = publishNotRetainedDuplicated(notAckPacketId, topic, qos, copiedPayload);
-                inflightTimeouts.add(new InFlightPacket(notAckPacketId.packetId, FLIGHT_BEFORE_RESEND_MS));
-                mqttConnection.sendPublish(publishMsg);
+            final SessionRegistry.PublishedMessage msg =
+                (SessionRegistry.PublishedMessage) inflightWindow.get(notAckPacketId.packetId);
+            if (msg == null) {
+                // Already acked...
+                continue;
             }
+            final Topic topic = msg.topic;
+            final MqttQoS qos = msg.publishingQos;
+            final ByteBuf payload = msg.payload;
+            final ByteBuf copiedPayload = payload.retainedDuplicate();
+            MqttPublishMessage publishMsg = publishNotRetainedDuplicated(notAckPacketId, topic, qos, copiedPayload);
+            inflightTimeouts.add(new InFlightPacket(notAckPacketId.packetId, FLIGHT_BEFORE_RESEND_MS));
+            mqttConnection.sendPublish(publishMsg);
         }
     }