diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 5b472c06837b1308b1c6539f470008624959b45d..ce044da2873a279b897da05e370d79171f155ee5 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,11 @@
+2008-01-01  Paolo Carlini  <pcarlini@suse.de>
+
+	PR libstdc++/34636
+	* include/parallel/algobase.h (lexicographical_compare_switch(...,
+	random_access_iterator_tag, random_access_iterator_tag)): Careful
+	with undereferenceable iterators.
+	* testsuite/25_algorithms/sort/34636.cc: New.
+
 2007-12-30  Paolo Carlini  <pcarlini@suse.de>
 
 	* include/std/tuple (_Tuple_impl<>::_Tuple_impl(typename
diff --git a/libstdc++-v3/include/parallel/algobase.h b/libstdc++-v3/include/parallel/algobase.h
index 8e9438d8a8d17e07fb61a0d996585811fdff223e..39e9062faae3c0e8130efd07cd2fe72a1dc26edd 100644
--- a/libstdc++-v3/include/parallel/algobase.h
+++ b/libstdc++-v3/include/parallel/algobase.h
@@ -215,13 +215,7 @@ namespace __parallel
 					   random_access_iterator_tag(), 
 					   random_access_iterator_tag());
 
-	    // Less because shorter.
-	    const bool lbs = mm.first == end1;
-
-	    // Less because differing elements less.
-	    const bool lbdel = pred(*mm.first, *mm.second);
-
-	    return lbs || lbdel;
+	    return (mm.first == end1) || bool(pred(*mm.first, *mm.second));
 	  }
 	else
 	  {
@@ -231,13 +225,7 @@ namespace __parallel
 					   random_access_iterator_tag(), 
 					   random_access_iterator_tag());
 
-	    // Less because shorter.
-	    const bool lbs = mm.first != end2;
-
-	    // Less because differing element less.
-	    const bool lbdel = pred(*mm.second, *mm.first);
-
-	    return lbs && lbdel;
+	    return (mm.first != end2) && bool(pred(*mm.second, *mm.first));
 	  }
       }
     else
diff --git a/libstdc++-v3/testsuite/25_algorithms/sort/34636.cc b/libstdc++-v3/testsuite/25_algorithms/sort/34636.cc
new file mode 100644
index 0000000000000000000000000000000000000000..61fa4d522479c1ad7eeff3d1ca72ea8d8ecad10e
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/sort/34636.cc
@@ -0,0 +1,33 @@
+// Copyright (C) 2007 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 2, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING.  If not, write to the Free
+// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+// USA.
+
+#include <vector>
+#include <algorithm>
+
+// libstdc++/34636
+void test01()
+{
+  std::vector<std::vector<int> > v(2);
+  std::sort(v.begin(), v.end()); 
+}
+
+int main()
+{
+  test01();
+  return 0;
+}