diff --git a/infrastructure-centred/owlps-listener/owlps-listenerd.c b/infrastructure-centred/owlps-listener/owlps-listenerd.c
index 0e93896..370304e 100644
--- a/infrastructure-centred/owlps-listener/owlps-listenerd.c
+++ b/infrastructure-centred/owlps-listener/owlps-listenerd.c
@@ -488,7 +488,8 @@ void read_packet(u_char *args, const struct pcap_pkthdr *header,
   struct iphdr *packet_ip_header = NULL ;
   // Pointer to the (possible) UDP header of the packet:
   struct udphdr *packet_udp_header = NULL ;
-  char packet_type ; // Localisation request type (request, calibration)
+  // Localisation request type (request, calibration, autocalibration):
+  unsigned char packet_type ;
   BOOL is_explicit_packet = TRUE ; // Is the packet an explicit request?
   int i ; // Iterator