diff -Nru /n/sources/plan9/sys/src/libcontrol/control.c /sys/src/libcontrol/control.c
--- /n/sources/plan9/sys/src/libcontrol/control.c	Fri Jul  2 16:14:50 2004
+++ /sys/src/libcontrol/control.c	Sun Nov  6 00:00:00 2016
@@ -343,9 +343,12 @@
 char*
 _ctlstrrune(Rune *r)
 {
+	int nb;
 	char *s;
-	s = ctlmalloc(runestrlen(r)*UTFmax+1);
-	sprint(s, "%S", r);
+
+	nb = runestrlen(r)*UTFmax+1;
+	s = ctlmalloc(nb);
+	snprint(s, nb, "%S", r);
 	return s;
 }
 
diff -Nru /n/sources/plan9/sys/src/libcontrol/scribble.c /sys/src/libcontrol/scribble.c
--- /n/sources/plan9/sys/src/libcontrol/scribble.c	Sun Aug  8 16:34:48 2004
+++ /sys/src/libcontrol/scribble.c	Sun Nov  6 00:00:00 2016
@@ -110,9 +110,9 @@
 	else if(r == ' ')
 		strcpy(b->lastchar, "' '");
 	else if(r < ' ')
-		sprint(b->lastchar, "ctl-%c", r+'@');
+		snprint(b->lastchar, sizeof b->lastchar, "ctl-%c", r+'@');
 	else
-		sprint(b->lastchar, "%C", r);
+		snprint(b->lastchar, sizeof b->lastchar, "%C", r);
 }