diff --git a/src/include/lwip/sys.h b/src/include/lwip/sys.h
index dc935133..fd45ee8a 100644
--- a/src/include/lwip/sys.h
+++ b/src/include/lwip/sys.h
@@ -184,7 +184,7 @@ err_t sys_mbox_trypost(sys_mbox_t *mbox, void *msg);
 /** Wait for a new message to arrive in the mbox
  * @param mbox mbox to get a message from
  * @param msg pointer where the message is stored
- * @param timeout maximum time (in milliseconds) to wait for a message
+ * @param timeout maximum time (in milliseconds) to wait for a message (0 = wait forever)
  * @return time (in milliseconds) waited for a message, may be 0 if not waited
            or SYS_ARCH_TIMEOUT on timeout
  *         The returned time has to be accurate to prevent timer jitter! */
@@ -194,7 +194,6 @@ u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout);
 /** Wait for a new message to arrive in the mbox
  * @param mbox mbox to get a message from
  * @param msg pointer where the message is stored
- * @param timeout maximum time (in milliseconds) to wait for a message
  * @return 0 (milliseconds) if a message has been received
  *         or SYS_MBOX_EMPTY if the mailbox is empty */
 u32_t sys_arch_mbox_tryfetch(sys_mbox_t *mbox, void **msg);