diff --git a/libowlps/libowlps.c b/libowlps/libowlps.c
index 3d8bfbf..d2300a5 100644
--- a/libowlps/libowlps.c
+++ b/libowlps/libowlps.c
@@ -137,7 +137,7 @@ uint_fast8_t owl_frequency_to_channel(const uint_fast16_t channel)
  * 'time_ms' is an unsigned value, so please be careful: passing a
  * negative value may not do what you think.
  * In case of error, a message is displayed and a non-zero error code
- * is returned.
+ * is returned (if positive, it is the number of non-sleeped seconds).
  */
 int owl_msleep(uint32_t time_ms)
 {
@@ -331,6 +331,7 @@ float owl_swap_float(const float f)
  *    description will be saved.
  *  - client_description (in/out): the structure in which the client
  *    description will be saved.
+ * Returns a negative error code in case of error.
  */
 int owl_create_udp_trx_socket(const char *const server_address,
                               const uint_fast16_t server_port,
@@ -344,7 +345,7 @@ int owl_create_udp_trx_socket(const char *const server_address,
   if (sockfd < 0)
     {
       perror("UDP socket creation failed") ;
-      return sockfd ;
+      return -OWL_ERR_SOCKET_CREATE ;
     }
 
   /* Initialise the client structure */
@@ -368,6 +369,7 @@ int owl_create_udp_trx_socket(const char *const server_address,
  * Creates a UDP reception socket and returns its descriptor.
  * Parameters:
  *  - port: port on which the socket listens.
+ * Returns a negative error code in case of error.
  */
 int owl_create_udp_listening_socket(const uint_fast16_t port)
 {
@@ -380,7 +382,7 @@ int owl_create_udp_listening_socket(const uint_fast16_t port)
   if (sockfd < 0)
     {
       perror("UDP socket creation failed") ;
-      return sockfd ;
+      return -OWL_ERR_SOCKET_CREATE ;
     }
 
   /* Initialise the server structure */
@@ -397,7 +399,7 @@ int owl_create_udp_listening_socket(const uint_fast16_t port)
     {
       perror("Cannot bind the UDP socket") ;
       close(sockfd) ;
-      return ret ;
+      return -OWL_ERR_SOCKET_CREATE ;
     }
 
   return sockfd ;