diff --git a/toxcore/Messenger.c b/toxcore/Messenger.c
index 9601f2a2..0efe20ce 100644
--- a/toxcore/Messenger.c
+++ b/toxcore/Messenger.c
@@ -357,6 +357,9 @@ int setfriendname(Messenger *m, int friendnumber, uint8_t *name, uint16_t length
     if (friend_not_valid(m, friendnumber))
         return -1;
 
+    if (length > MAX_NAME_LENGTH || length == 0)
+        return -1;
+
     m->friendlist[friendnumber].name_length = length;
     memcpy(m->friendlist[friendnumber].name, name, length);
     return 0;
diff --git a/toxcore/Messenger.h b/toxcore/Messenger.h
index 1f0361b1..0ff14de4 100644
--- a/toxcore/Messenger.h
+++ b/toxcore/Messenger.h
@@ -247,6 +247,9 @@ uint32_t m_sendmessage_withid(Messenger *m, int friendnumber, uint32_t theid, ui
 int m_sendaction(Messenger *m, int friendnumber, uint8_t *action, uint32_t length);
 
 /* Set the name and name_length of a friend.
+ * name must be a string of maximum MAX_NAME_LENGTH length.
+ * length must be at least 1 byte.
+ * length is the length of name with the NULL terminator.
  *
  *  return 0 if success.
  *  return -1 if failure.