diff --git a/sys/teken/sequences b/sys/teken/sequences
index 957665a02f53..cf720b0ca0f9 100644
--- a/sys/teken/sequences
+++ b/sys/teken/sequences
@@ -88,6 +88,7 @@ ICH	Insert character			^[ [ @		n
 IL	Insert line				^[ [ L		n
 IND	Index					^[ D
 NEL	Next line				^[ E
+OSC	Operating System Command		^[ ]
 RI	Reverse index				^[ M
 RIS	Reset to Initial State			^[ c
 RM	Reset Mode				^[ [ l		r
diff --git a/sys/teken/teken.c b/sys/teken/teken.c
index c8d6b09cc33a..81b8ac08f812 100644
--- a/sys/teken/teken.c
+++ b/sys/teken/teken.c
@@ -56,6 +56,7 @@ static FILE *df;
 #define	TS_WRAPPED	0x10	/* Next character should be printed on col 0. */
 #define	TS_8BIT		0x20	/* UTF-8 disabled. */
 #define	TS_CONS25	0x40	/* cons25 emulation. */
+#define	TS_INSTRING	0x80	/* Inside string. */
 
 /* Character that blanks a cell. */
 #define	BLANK	' '
@@ -176,6 +177,24 @@ static void
 teken_input_char(teken_t *t, teken_char_t c)
 {
 
+	/*
+	 * There is no support for DCS and OSC.  Just discard strings
+	 * until we receive characters that may indicate string
+	 * termination.
+	 */
+	if (t->t_stateflags & TS_INSTRING) {
+		switch (c) {
+		case '\x1B':
+			t->t_stateflags &= ~TS_INSTRING;
+			break;
+		case '\a':
+			t->t_stateflags &= ~TS_INSTRING;
+			return;
+		default:
+			return;
+		}
+	}
+
 	switch (c) {
 	case '\0':
 		break;
diff --git a/sys/teken/teken_subr.h b/sys/teken/teken_subr.h
index b8ebcdc13026..ad10abbb6fd5 100644
--- a/sys/teken/teken_subr.h
+++ b/sys/teken/teken_subr.h
@@ -425,10 +425,11 @@ teken_subr_delete_line(teken_t *t, unsigned int nrows)
 }
 
 static void
-teken_subr_device_control_string(teken_t *t __unused)
+teken_subr_device_control_string(teken_t *t)
 {
 
-	teken_printf("device control string???\n");
+	teken_printf("Unsupported device control string\n");
+	t->t_stateflags |= TS_INSTRING;
 }
 
 static void
@@ -743,6 +744,14 @@ teken_subr_next_line(teken_t *t)
 	teken_subr_newline(t);
 }
 
+static void
+teken_subr_operating_system_command(teken_t *t)
+{
+
+	teken_printf("Unsupported operating system command\n");
+	t->t_stateflags |= TS_INSTRING;
+}
+
 static void
 teken_subr_pan_down(teken_t *t, unsigned int nrows)
 {
@@ -1258,7 +1267,10 @@ static void
 teken_subr_string_terminator(teken_t *t __unused)
 {
 
-	teken_printf("string terminator???\n");
+	/*
+	 * Strings are already terminated in teken_input_char() when ^[
+	 * is inserted.
+	 */
 }
 
 static void