diff --git a/core/net/mac/mac.c b/core/net/mac/mac.c
index c79b75665..bdb7b6f2f 100644
--- a/core/net/mac/mac.c
+++ b/core/net/mac/mac.c
@@ -45,7 +45,7 @@ void
 mac_call_sent_callback(mac_callback_t sent, void *ptr, int status, int num_tx)
 {
   PRINTF("mac_callback_t %p ptr %p status %d num_tx %d\n",
-         sent, ptr, status, num_tx);
+         (void *)sent, ptr, status, num_tx);
   switch(status) {
   case MAC_TX_COLLISION:
     PRINTF("mac: collision after %d tx\n", num_tx);