diff --git a/toxcore/Messenger.c b/toxcore/Messenger.c
index 9863018d..6b691ad8 100644
--- a/toxcore/Messenger.c
+++ b/toxcore/Messenger.c
@@ -161,6 +161,12 @@ static int m_handle_lossy_packet(void *object, int friend_num, const uint8_t *pa
 
 static int32_t init_new_friend(Messenger *m, const uint8_t *real_pk, uint8_t status)
 {
+    if (m->numfriends == UINT32_MAX) {
+        LOGGER_ERROR(m->log, "Friend list full: we have more than 4 billion friends");
+        /* This is technically incorrect, but close enough. */
+        return FAERR_NOMEM;
+    }
+
     /* Resize the friend list if necessary. */
     if (realloc_friendlist(m, m->numfriends + 1) != 0) {
         return FAERR_NOMEM;