Hi,

So the machine that has this error has the following properties:

Distro: Debian Stretch

``` sources.list
deb http://ftp.de.debian.org/debian/ stretch main
deb-src http://ftp.de.debian.org/debian/ stretch main

deb http://security.debian.org/debian-security stretch/updates main
deb-src http://security.debian.org/debian-security stretch/updates main

# stretch-updates, previously known as 'volatile'
deb http://ftp.de.debian.org/debian/ stretch-updates main
deb-src http://ftp.de.debian.org/debian/ stretch-updates main
```

Bug still apears after: `apt update && apt upgrade -y`

`uname -a` returns:
```
Linux <hostname> 4.9.0-8-amd64 #1 SMP Debian 4.9.130-2 (2018-10-27)
x86_64 GNU/Linux
```
(I substituted the real hostname with <hostname>)

Loaded Xorg modules:

`grep LoadModule /var/log/Xorg.0.log`
```
[    11.843] (II) LoadModule: "glx"
[    11.856] (II) LoadModule: "ati"
[    11.857] (II) LoadModule: "radeon"
[    11.860] (II) LoadModule: "modesetting"
[    11.861] (II) LoadModule: "fbdev"
[    11.861] (II) LoadModule: "vesa"
[    11.870] (II) LoadModule: "fbdevhw"
[    11.872] (II) LoadModule: "fb"
[    11.873] (II) LoadModule: "dri2"
[    11.874] (II) LoadModule: "glamoregl"
[    12.394] (II) LoadModule: "ramdac"
[    12.705] (II) LoadModule: "libinput"
```

The bug still appears after pulling a new version of guix (e5ad2cdf1):

`guix environment --ad-hoc teeworlds -- teeworlds` for example
SEGFAULTs.

I hope this information helps reproducing the bug.

Tim.