diff --git a/pasp-mode.el b/pasp-mode.el
index 7f83645..5daf08e 100644
--- a/pasp-mode.el
+++ b/pasp-mode.el
@@ -199,9 +199,12 @@
 Argument ENCODING The current buffer which holds the problem encoding.
 Optional argument INSTANCE The problem instance which is solved by the encoding.
   If no instance it is assumed to be also in the encoding file."
-  (if 'instance
-      (concat pasp-clingo-path " " pasp-clingo-options " " encoding " " instance)
-    (concat pasp-clingo-path " " pasp-clingo-options " " encoding)))
+  (if instance
+      (concat pasp-clingo-path " " pasp-clingo-options " "
+              (shell-quote-argument encoding) " "
+              (shell-quote-argument instance))
+    (concat pasp-clingo-path " " pasp-clingo-options " "
+            (shell-quote-argument encoding))))
 
 (defun pasp-run-clingo (encoding &optional instance)
   "Run Clingo with some ASP input files.
ix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=9d53c236a69786508197c75d42923e8891c9212d'>refs</a><a class='active' href='/guix/log/HACKING'>log</a><a href='/guix/tree/HACKING?id=9d53c236a69786508197c75d42923e8891c9212d'>tree</a><a href='/guix/commit/HACKING?id=9d53c236a69786508197c75d42923e8891c9212d'>commit</a><a href='/guix/diff/HACKING?id=9d53c236a69786508197c75d42923e8891c9212d'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/HACKING'>
<input type='hidden' name='id' value='9d53c236a69786508197c75d42923e8891c9212d'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=9d53c236a69786508197c75d42923e8891c9212d'>root</a>/<a href='/guix/log/HACKING?id=9d53c236a69786508197c75d42923e8891c9212d'>HACKING</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/HACKING?id=9d53c236a69786508197c75d42923e8891c9212d&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-10-23 12:57:20 -0400'>2020-10-23</span></td><td><a href='/guix/commit/HACKING?id=73faee9fb25465f1b236f5f94e1052145655736f'>doc: Fix typo in HACKING.</a><span class='msg-avail'>...<span class='msg-tooltip'>* HACKING (Contributing): s/informations/information/.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-01-09 23:33:04 +0100'>2020-01-09</span></td><td><a href='/guix/commit/HACKING?id=2d315cd428484537e763d7f7c676dc5fff7995f6'>doc: Move "Commit Access" section from 'HACKING' to the manual.</a><span class='msg-avail'>...<span class='msg-tooltip'>* HACKING (Commit Access): Remove.
(Contributing): Update URL of the manual.
* doc/contributing.texi (Commit Access): New section.
(Submitting Patches): Add cross reference.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-01-09 23:33:04 +0100'>2020-01-09</span></td><td><a href='/guix/commit/HACKING?id=a7bde77d247ed0765f5378779d67b4668c5d7648'>doc: Add "Tracking Bugs and Patches" section.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/contributing.texi (Tracking Bugs and Patches): New section.
(Submitting Patches): Refer to it.
* doc/guix.texi: Update copyright line.
* HACKING (Using emacs-debbugs): Remove.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-07-13 14:25:19 -0400'>2019-07-13</span></td><td><a href='/guix/commit/HACKING?id=06e1ecbf17fee7fe513ad2808d8175fb3565ae3e'>doc: Update keyserver URL.</a><span class='msg-avail'>...<span class='msg-tooltip'>* HACKING (Commit Access): Change keyserver URL to 'keys.openpgp.org'.
</span></span></td><td>Leo Famulari</td></tr>