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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<tr><td><span title='2020-09-05 22:30:04 +0300'>2020-09-05</span></td><td><a href='/guix/commit/gnu/packages/wget.scm?id=de3c03a47160dec355d9b19ad5ca210d90c15fd7'>Merge remote-tracking branch 'origin/master' into staging</a></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-09-01 04:44:34 +0200'>2020-09-01</span></td><td><a href='/guix/commit/gnu/packages/wget.scm?id=30714da09a50bf20780e9903104e29c930da855a'>gnu: wgetpaste: Update bpaste URL &amp; regular expressions.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/wget.scm (wgetpaste)[source]: Add patch.
* gnu/packages/patches/wgetpaste-update-bpaste.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-09-01 04:44:34 +0200'>2020-09-01</span></td><td><a href='/guix/commit/gnu/packages/wget.scm?id=7b88396febe35e05bb4f67ed609204c8533314d8'>gnu: wgetpaste: Update to 2.30.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/wget.scm (wgetpaste): Update to 2.30.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-09-01 04:44:34 +0200'>2020-09-01</span></td><td><a href='/guix/commit/gnu/packages/wget.scm?id=1b0755012b38fded6059c10849dc16e3e50ed8b8'>gnu: wgetpaste: Use HTTPS home page.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/wget.scm (wgetpaste)[source, home-page]: Use HTTPS.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-09-01 04:44:34 +0200'>2020-09-01</span></td><td><a href='/guix/commit/gnu/packages/wget.scm?id=57ea4dfca1212687213a2db8cd47addf85e2ea3f'>gnu: wgetpaste: Fix historical confusion.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/wget.scm (wgetpaste)[arguments]: Fix the reversed
substitution and clarify its purpose.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-07-03 10:56:21 +0200'>2020-07-03</span></td><td><a href='/guix/commit/gnu/packages/wget.scm?id=8a6898b60173ff9c70f53a5641335c2e99d51a7e'>gnu: wget: Cross-build fix.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/wget.scm (wget)[inputs]: Move lzip to ...
[native-inputs]: ... here.
</span></span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>