diff --git a/core/net/nbr-table.c b/core/net/nbr-table.c
index 74028d573..f5d53c333 100644
--- a/core/net/nbr-table.c
+++ b/core/net/nbr-table.c
@@ -157,7 +157,7 @@ nbr_set_bit(uint8_t *bitmap, nbr_table_t *table, nbr_table_item_t *item, int val
 }
 /*---------------------------------------------------------------------------*/
 static nbr_table_key_t *
-nbr_table_allocate()
+nbr_table_allocate(void)
 {
   nbr_table_key_t *key;
   int least_used_count = 0;
diff --git a/core/net/rpl/rpl-dag.c b/core/net/rpl/rpl-dag.c
index 220d9facc..3b1e01c73 100644
--- a/core/net/rpl/rpl-dag.c
+++ b/core/net/rpl/rpl-dag.c
@@ -79,7 +79,7 @@ rpl_instance_t instance_table[RPL_MAX_INSTANCES];
 rpl_instance_t *default_instance;
 /*---------------------------------------------------------------------------*/
 void
-rpl_dag_init()
+rpl_dag_init(void)
 {
   nbr_table_register(rpl_parents, (nbr_table_callback *)rpl_remove_parent);
 }
diff --git a/core/net/uip-ds6-nbr.c b/core/net/uip-ds6-nbr.c
index 1826285c1..22d3a9f3c 100644
--- a/core/net/uip-ds6-nbr.c
+++ b/core/net/uip-ds6-nbr.c
@@ -200,10 +200,9 @@ uip_ds6_link_neighbor_callback(int status, int numtx)
 #endif /* UIP_DS6_LL_NUD */
 
 }
-
 /*---------------------------------------------------------------------------*/
 void
-uip_ds6_neighbor_periodic()
+uip_ds6_neighbor_periodic(void)
 {
   /* Periodic processing on neighbors */
   uip_ds6_nbr_t *nbr = nbr_table_head(ds6_neighbors);