diff --git a/apps/er-coap-03/er-coap-03-observing.c b/apps/er-coap-03/er-coap-03-observing.c
index a55c31691..fe23f5d03 100644
--- a/apps/er-coap-03/er-coap-03-observing.c
+++ b/apps/er-coap-03/er-coap-03-observing.c
@@ -122,7 +122,7 @@ coap_remove_observer_by_token(uip_ipaddr_t *addr, uint16_t port, uint8_t *token,
 }
 /*-----------------------------------------------------------------------------------*/
 void
-coap_notify_observers(resource_t *resource, uint16_t obs_counter, void *notification)
+coap_notify_observers(resource_t *resource, int32_t obs_counter, void *notification)
 {
   coap_packet_t *const coap_res = (coap_packet_t *) notification;
   coap_observer_t* obs = NULL;
diff --git a/apps/er-coap-03/er-coap-03-observing.h b/apps/er-coap-03/er-coap-03-observing.h
index 48cae5f92..cde1974ae 100644
--- a/apps/er-coap-03/er-coap-03-observing.h
+++ b/apps/er-coap-03/er-coap-03-observing.h
@@ -69,7 +69,7 @@ coap_observer_t *coap_add_observer(uip_ipaddr_t *addr, uint16_t port, const uint
 void coap_remove_observer(coap_observer_t *o);
 int coap_remove_observer_by_client(uip_ipaddr_t *addr, uint16_t port);
 int coap_remove_observer_by_token(uip_ipaddr_t *addr, uint16_t port, uint8_t *token, size_t token_len);
-void coap_notify_observers(resource_t *resource, uint16_t obs_counter, void *notification);
+void coap_notify_observers(resource_t *resource, int32_t obs_counter, void *notification);
 
 void coap_observe_handler(resource_t *resource, void *request, void *response);
 
diff --git a/apps/er-coap-07/er-coap-07-observing.c b/apps/er-coap-07/er-coap-07-observing.c
index 23fae45c4..af93492f4 100644
--- a/apps/er-coap-07/er-coap-07-observing.c
+++ b/apps/er-coap-07/er-coap-07-observing.c
@@ -167,7 +167,7 @@ coap_remove_observer_by_mid(uip_ipaddr_t *addr, uint16_t port, uint16_t mid)
 }
 /*-----------------------------------------------------------------------------------*/
 void
-coap_notify_observers(resource_t *resource, uint16_t obs_counter, void *notification)
+coap_notify_observers(resource_t *resource, int32_t obs_counter, void *notification)
 {
   coap_packet_t *const coap_res = (coap_packet_t *) notification;
   coap_observer_t* obs = NULL;
diff --git a/apps/er-coap-07/er-coap-07-observing.h b/apps/er-coap-07/er-coap-07-observing.h
index a17ad86bd..62f9f7df4 100644
--- a/apps/er-coap-07/er-coap-07-observing.h
+++ b/apps/er-coap-07/er-coap-07-observing.h
@@ -75,7 +75,7 @@ int coap_remove_observer_by_token(uip_ipaddr_t *addr, uint16_t port, uint8_t *to
 int coap_remove_observer_by_url(uip_ipaddr_t *addr, uint16_t port, const char *url);
 int coap_remove_observer_by_mid(uip_ipaddr_t *addr, uint16_t port, uint16_t mid);
 
-void coap_notify_observers(resource_t *resource, uint16_t obs_counter, void *notification);
+void coap_notify_observers(resource_t *resource, int32_t obs_counter, void *notification);
 
 void coap_observe_handler(resource_t *resource, void *request, void *response);