diff -r 2447a1b462c2 sys/src/cmd/tee.c
--- a/sys/src/cmd/tee.c Thu Apr 12 17:50:10 2018 -0400
+++ b/sys/src/cmd/tee.c Tue Apr 17 14:44:52 2018 -0700
@@ -13,6 +13,7 @@
 int    aflag;
 
 char in[8192];
+int fds[128];
 
 int    intignore(void*, char*);
 
@@ -54,9 +55,9 @@
                if(i < 0) {
                        fprint(2, "tee: cannot open %s: %r\n", argv[0]);
                } else {
-                       if(i != n+FDSTART)
-                               dup(i, n+FDSTART);
-                       n++;
+                       if (n == nelem(fds))
+                               fprint(2, "tee: too many fds\n");
+                       fds[n++] = i;
                }
                argv++;
        }
@@ -66,7 +67,7 @@
                if(r <= 0)
                        exits(nil);
                for(i=0; i<n; i++)
-                       write(i+FDSTART, in, r);
+                       write(fds[i], in, r);
                write(1, in, r);
        }
 }