diff --git a/src/hoaparse/hoascan.ll b/src/hoaparse/hoascan.ll
index 95eef0e04..6a85a21e9 100644
--- a/src/hoaparse/hoascan.ll
+++ b/src/hoaparse/hoascan.ll
@@ -362,8 +362,6 @@ namespace spot
     // yy_flex_debug = 1;
     if (name == "-")
       {
-        yyin = stdin;
-
         // If the input is a pipe, make the scanner
         // interactive so that it does not wait for the input
         // buffer to be full to process automata.
@@ -372,6 +370,10 @@ namespace spot
            throw std::runtime_error("fstat failed");
 	if (S_ISFIFO(s.st_mode))
 	  want_interactive = true;
+
+	// Only set yyin once we know we will use
+	// it, so that we do not close it otherwise.
+        yyin = stdin;
       }
     else
       {
@@ -395,6 +397,9 @@ namespace spot
 
     yyin = fdopen(fd, "r");
 
+    if (!yyin)
+      throw std::runtime_error("fdopen failed");
+
     // If the input is a pipe, make the scanner
     // interactive so that it does not wait for the input
     // buffer to be full to process automata.
@@ -416,6 +421,10 @@ namespace spot
   void
   hoayyclose()
   {
-    fclose(yyin);
+    if (yyin)
+      {
+	fclose(yyin);
+	yyin = NULL;
+      }
   }
 }
diff --git a/wrap/python/spot.py b/wrap/python/spot.py
index 3427be03d..ba1706c59 100644
--- a/wrap/python/spot.py
+++ b/wrap/python/spot.py
@@ -137,6 +137,7 @@ def automata(*filenames):
 
     for filename in filenames:
         try:
+            p = None
             if filename[-1] != '|':
                 proc = None
                 p = hoa_stream_parser(filename, True)
diff --git a/wrap/python/tests/automata-io.ipynb b/wrap/python/tests/automata-io.ipynb
index 1d096d370..67557afe5 100644
--- a/wrap/python/tests/automata-io.ipynb
+++ b/wrap/python/tests/automata-io.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:8a904efb232462e4b08337adba95ad1f6c71494bad4a9d4b3872cbbb3bec76d6"
+  "signature": "sha256:becf15ababe000c66fc9b2c6cf5e829f92966efe6b75b2ac2191806dc013a48e"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -161,7 +161,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f156825d240> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fdad87e36f0> >"
        ]
       }
      ],
@@ -272,7 +272,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f156825d210> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fdad87e37b0> >"
        ]
       },
       {
@@ -329,7 +329,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f156825d420> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fdad87e3960> >"
        ]
       }
      ],
@@ -448,7 +448,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f156825d630> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fdad87e3ba0> >"
        ]
       }
      ],
@@ -563,7 +563,7 @@
         "</svg>\n"
        ],
        "text": [
-        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7f156825d510> >"
+        "<spot_impl.tgba_digraph; proxy of <Swig Object of type 'std::shared_ptr< spot::tgba_digraph > *' at 0x7fdad87e3d20> >"
        ]
       },
       {
@@ -587,6 +587,63 @@
      "metadata": {},
      "outputs": [],
      "prompt_number": 10
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "spot.automaton('example.aut')"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "ename": "RuntimeError",
+       "evalue": "Cannot open file example.aut",
+       "output_type": "pyerr",
+       "traceback": [
+        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mRuntimeError\u001b[0m                              Traceback (most recent call last)",
+        "\u001b[0;32m<ipython-input-11-91499c480122>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mspot\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mautomaton\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'example.aut'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+        "\u001b[0;32m/home/adl/git/spot/wrap/python/spot.py\u001b[0m in \u001b[0;36mautomaton\u001b[0;34m(filename)\u001b[0m\n\u001b[1;32m    169\u001b[0m     See `spot.automata()` for a list of supported format.\"\"\"\n\u001b[1;32m    170\u001b[0m     \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 171\u001b[0;31m         \u001b[0;32mreturn\u001b[0m \u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mautomata\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mfilename\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    172\u001b[0m     \u001b[0;32mexcept\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    173\u001b[0m         \u001b[0;32mraise\u001b[0m \u001b[0mRuntimeError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"Failed to read automaton from {}\"\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mformat\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mfilename\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
+        "\u001b[0;32m/home/adl/git/spot/wrap/python/spot.py\u001b[0m in \u001b[0;36mautomata\u001b[0;34m(*filenames)\u001b[0m\n\u001b[1;32m    141\u001b[0m             \u001b[0;32mif\u001b[0m \u001b[0mfilename\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m-\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m!=\u001b[0m \u001b[0;34m'|'\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    142\u001b[0m                 \u001b[0mproc\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;32mNone\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 143\u001b[0;31m                 \u001b[0mp\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mhoa_stream_parser\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mfilename\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;32mTrue\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    144\u001b[0m             \u001b[0;32melse\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    145\u001b[0m                 proc = subprocess.Popen(filename[:-1], shell=True,\n",
+        "\u001b[0;32m/home/adl/git/spot/wrap/python/spot_impl.py\u001b[0m in \u001b[0;36m__init__\u001b[0;34m(self, *args)\u001b[0m\n\u001b[1;32m   2206\u001b[0m     \u001b[0m__repr__\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0m_swig_repr\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   2207\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__init__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m*\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 2208\u001b[0;31m         \u001b[0mthis\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0m_spot_impl\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mnew_hoa_stream_parser\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m*\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   2209\u001b[0m         \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mthis\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mappend\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mthis\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   2210\u001b[0m         \u001b[0;32mexcept\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mthis\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mthis\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
+        "\u001b[0;31mRuntimeError\u001b[0m: Cannot open file example.aut"
+       ]
+      }
+     ],
+     "prompt_number": 11
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "spot.automaton('non-existing-cmd |')"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "ename": "RuntimeError",
+       "evalue": "Command non-existing-cmd  exited with exit status 127",
+       "output_type": "pyerr",
+       "traceback": [
+        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mRuntimeError\u001b[0m                              Traceback (most recent call last)",
+        "\u001b[0;32m<ipython-input-12-2b2d1b66dcd6>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mspot\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mautomaton\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m'non-existing-cmd |'\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+        "\u001b[0;32m/home/adl/git/spot/wrap/python/spot.py\u001b[0m in \u001b[0;36mautomaton\u001b[0;34m(filename)\u001b[0m\n\u001b[1;32m    169\u001b[0m     See `spot.automata()` for a list of supported format.\"\"\"\n\u001b[1;32m    170\u001b[0m     \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 171\u001b[0;31m         \u001b[0;32mreturn\u001b[0m \u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mautomata\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mfilename\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    172\u001b[0m     \u001b[0;32mexcept\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    173\u001b[0m         \u001b[0;32mraise\u001b[0m \u001b[0mRuntimeError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"Failed to read automaton from {}\"\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mformat\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mfilename\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
+        "\u001b[0;32m/home/adl/git/spot/wrap/python/spot.py\u001b[0m in \u001b[0;36mautomata\u001b[0;34m(*filenames)\u001b[0m\n\u001b[1;32m    161\u001b[0m                 \u001b[0;32mif\u001b[0m \u001b[0mret\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    162\u001b[0m                     raise RuntimeError(\"Command {} exited with exit status {}\"\n\u001b[0;32m--> 163\u001b[0;31m                                        .format(filename[:-1], ret))\n\u001b[0m\u001b[1;32m    164\u001b[0m     \u001b[0;32mreturn\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    165\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
+        "\u001b[0;31mRuntimeError\u001b[0m: Command non-existing-cmd  exited with exit status 127"
+       ]
+      }
+     ],
+     "prompt_number": 12
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
     }
    ],
    "metadata": {}
diff --git a/wrap/python/tests/run.in b/wrap/python/tests/run.in
index 0942da19f..a7ad71f99 100755
--- a/wrap/python/tests/run.in
+++ b/wrap/python/tests/run.in
@@ -41,13 +41,15 @@ test -z "$1" &&
 case $1 in
   *.ipynb)
     PYTHONPATH=$pypath DYLD_LIBRARY_PATH=$modpath \
-    exec @PYTHON@ @srcdir@/ipnbdoctest.py "$@";;
+    exec $PREFIXCMD @PYTHON@ @srcdir@/ipnbdoctest.py "$@";;
   *.py)
-    PYTHONPATH=$pypath DYLD_LIBRARY_PATH=$modpath exec @PYTHON@ "$@";;
+    PYTHONPATH=$pypath DYLD_LIBRARY_PATH=$modpath \
+    exec $PREFIXCMD @PYTHON@ "$@";;
   *.test)
     exec sh -x "$@";;
   *python*)
-    PYTHONPATH=$pypath DYLD_LIBRARY_PATH=$modpath exec "$@";;
+    PYTHONPATH=$pypath DYLD_LIBRARY_PATH=$modpath \
+    exec $PREFIXCMD "$@";;
   *)
     echo "Unknown extension" >&2
     exit 2;;