Index: sys/kern/tty_ttydisc.c
===================================================================
--- sys/kern/tty_ttydisc.c
+++ sys/kern/tty_ttydisc.c
@@ -844,6 +844,7 @@
 					 */
 					ttyinq_write(&tp->t_inq, bytes,
 					    UTF8_STACKBUF, 0);
+					ttyinq_unputchar(&tp->t_inq);
 				} else {
 					/* Find codepoint and width. */
 					codepoint =
@@ -861,6 +862,7 @@
 						 */
 						ttyinq_write(&tp->t_inq, bytes,
 						    nb, 0);
+						ttyinq_unputchar(&tp->t_inq);
 					}
 				}
 				tp->t_column -= cwidth;
Index: sys/teken/teken_wcwidth.h
===================================================================
--- sys/teken/teken_wcwidth.h
+++ sys/teken/teken_wcwidth.h
@@ -128,8 +128,11 @@
 teken_utf8_bytes_to_codepoint(uint8_t bytes[4], int nbytes)
 {
 
-  /* Check for malformed characters. */
-  if (bitcount(bytes[0] & 0xf0) != nbytes)
+  /*
+   * Check for malformed characters by comparing 'nbytes' to
+   * the number of consecutive bits set starting from the MSB.
+   */
+  if (__builtin_clz(~(bytes[0] & 0xf0) << 24) != nbytes)
     return (TEKEN_UTF8_INVALID_CODEPOINT);
 
   switch (nbytes) {