diff --git a/libraries/AP_IRLock/AP_IRLock_SITL.cpp b/libraries/AP_IRLock/AP_IRLock_SITL.cpp
index 3ff5b28ac4..f02d52d6ef 100644
--- a/libraries/AP_IRLock/AP_IRLock_SITL.cpp
+++ b/libraries/AP_IRLock/AP_IRLock_SITL.cpp
@@ -62,19 +62,18 @@ bool AP_IRLock_SITL::update()
     // receive packet from Gazebo IRLock plugin
     irlock_packet pkt;
     const int wait_ms = 0;
-    size_t s = sock.recv(&pkt, sizeof(irlock_packet), wait_ms);
+    ssize_t s = sock.recv(&pkt, sizeof(irlock_packet), wait_ms);
 
     bool new_data = false;
-    
-    // fprintf(stderr, "sitl %d %d\n", i, _num_targets);
-    if (s == sizeof(irlock_packet) && pkt.timestamp/1000 > _last_timestamp) {
+
+    if (s == sizeof(irlock_packet) && pkt.timestamp > _last_timestamp) {
         // fprintf(stderr, "     posx %f posy %f sizex %f sizey %f\n", pkt.pos_x, pkt.pos_y, pkt.size_x, pkt.size_y);
-        _target_info.timestamp = pkt.timestamp / 1000;
+        _target_info.timestamp = pkt.timestamp;
         _target_info.pos_x = pkt.pos_x;
         _target_info.pos_y = pkt.pos_y;
         _target_info.size_x = pkt.size_x;
         _target_info.size_y = pkt.size_y;
-        _last_timestamp = pkt.timestamp/1000;
+        _last_timestamp = pkt.timestamp;
         _last_update_ms = _last_timestamp;
         new_data = true;
     }
diff --git a/libraries/AP_IRLock/AP_IRLock_SITL.h b/libraries/AP_IRLock/AP_IRLock_SITL.h
index 2d7a8aa00e..2f5d5cd4bc 100644
--- a/libraries/AP_IRLock/AP_IRLock_SITL.h
+++ b/libraries/AP_IRLock/AP_IRLock_SITL.h
@@ -27,7 +27,7 @@ private:
       reply packet sent from simulator to ArduPilot
      */
     struct irlock_packet {
-        uint64_t timestamp;
+        uint64_t timestamp;  // in miliseconds
         uint16_t num_targets;
         float pos_x;
         float pos_y;