diff --git a/src/core/dhcp.c b/src/core/dhcp.c
index cd6f1bd9..634ec4ec 100644
--- a/src/core/dhcp.c
+++ b/src/core/dhcp.c
@@ -349,7 +349,7 @@ dhcp_select(struct netif *netif)
  * The DHCP timer that checks for lease renewal/rebind timeouts.
  */
 void
-dhcp_coarse_tmr()
+dhcp_coarse_tmr(void)
 {
   struct netif *netif = netif_list;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_coarse_tmr()\n"));
@@ -387,7 +387,7 @@ dhcp_coarse_tmr()
  * This timer checks whether an outstanding DHCP request is timed out.
  */
 void
-dhcp_fine_tmr()
+dhcp_fine_tmr(void)
 {
   struct netif *netif = netif_list;
   /* loop through netif's */
diff --git a/src/core/ipv4/autoip.c b/src/core/ipv4/autoip.c
index 1407ab9e..4837df2f 100644
--- a/src/core/ipv4/autoip.c
+++ b/src/core/ipv4/autoip.c
@@ -384,7 +384,7 @@ autoip_stop(struct netif *netif)
  * Has to be called in loop every AUTOIP_TMR_INTERVAL milliseconds
  */
 void
-autoip_tmr()
+autoip_tmr(void)
 {
   struct netif *netif = netif_list;
   /* loop through netif's */