diff --git a/tty-keys.c b/tty-keys.c
index 7f9e8352..8fc51174 100644
--- a/tty-keys.c
+++ b/tty-keys.c
@@ -1389,7 +1389,7 @@ tty_keys_clipboard(struct tty *tty, const char *buf, size_t len, size_t *size)
 		return (0);
 	}
 	out = xmalloc(needed);
-	if ((outlen = b64_pton(copy, out, len)) == -1) {
+	if ((outlen = b64_pton(copy, out, needed)) == -1) {
 		free(out);
 		free(copy);
 		return (0);