i3 says "could not create graphical context" with TigerVNC on NixOS

Output of i3 --moreversion 2>&- || i3 --version:

Binary i3 version: 4.13 (2016-11-08) © 2009 Michael Stapelberg and contributors

URL to a logfile as per http://i3wm.org/docs/debugging.html:

http://logs.i3wm.org/logs/5637337312657408.bz2

What I did:

Install tigervnc, then do

cat > ~/.vnc/xstartup <<EOF
#!/bin/sh
exec i3
EOF
chmod +x ~/.vnc/xstartup
vncserver

What I saw:

sean@loefah ~> cat .vnc/loefah:1.log                                                                      

Xvnc TigerVNC 1.7.80 - built Jan  1 1970 00:00:01
Copyright (C) 1999-2016 TigerVNC Team and many others (see README.txt)
See http://www.tigervnc.org for information on TigerVNC.
Underlying X server release 11902000, The X.Org Foundation


Thu Apr  6 16:20:19 2017
 vncext:      VNC extension running!
 vncext:      Listening for VNC connections on all interface(s), port 5901
 vncext:      created VNC server for screen 0
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
04/06/2017 04:20:22 PM - [libi3] ERROR: Could not create graphical context. Error code: 9. Please report this bug.
i3status: trying to auto-detect output_format setting
i3status: auto-detected "i3bar"
Could not grab keyboard, status = 3
[libi3] libi3/font.c Using Pango font monospace, size 8
[libi3] libi3/font.c X11 root window dictates 96.094581 DPI
[libi3] libi3/font.c Using Pango font monospace, size 8

What I expected instead: A working VNC session using i3.