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.
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<div class='path'>path: <a href='/guix/log/?id=dc7e57833e6817adb9c799b2fda8b10921f1b050'>root</a>/<a href='/guix/log/tests?id=dc7e57833e6817adb9c799b2fda8b10921f1b050'>tests</a>/<a href='/guix/log/tests/cache.scm?id=dc7e57833e6817adb9c799b2fda8b10921f1b050'>cache.scm</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/tests/cache.scm?id=dc7e57833e6817adb9c799b2fda8b10921f1b050&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-04-22 14:42:15 +0200'>2017-04-22</span></td><td><a href='/guix/commit/tests/cache.scm?id=25a49294caf2386e65fc1b12a2508324be0b1cc2'>cache: Work around 'time-monotonic' bug in Guile 2.2.2.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/cache.scm (time-monotonic) [guile-2.2]: New variable.
* tests/cache.scm (time-monotonic) [guile-2.2]: Likewise.
* guix/build/download.scm (time-monotonic) [guile-2.2]: Adjust comment:
it's a 2.2.2 bug.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-04-18 23:19:30 +0200'>2017-04-18</span></td><td><a href='/guix/commit/tests/cache.scm?id=2ea2aac6e9d58a07c029504f94fb5015cd407e31'>Add (guix cache) and use it in (guix scripts substitute).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/cache.scm, tests/cache.scm: New files.
* Makefile.am (MODULES, SCM_TESTS): Add them.
* guix/scripts/substitute.scm (obsolete?): Remove.
(remove-expired-cached-narinfos): Rename to...
(cached-narinfo-expiration-time): ... this.  Remove the removal part and
only keep the expiration time part.
(narinfo-cache-directories): Add optional 'directory' parameter and
honor it.
(maybe-remove-expired-cached-narinfo): Remove.
(cached-narinfo-files): New procedure.
(guix-substitute): Use 'maybe-remove-expired-cache-entries' instead of
'maybe-remove-expired-cached-narinfo'.
</span></span></td><td>Ludovic Courtès</td></tr>