diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index eb9936f423b..ab12fae5382 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,15 @@
+2012-04-13  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	* include/debug/safe_iterator.h (_BeforeBeginHelper<>::
+	_S_Is_Beginnest): Add.
+	* include/debug/forward_list (_BeforeBeginHelper<>::
+	_S_Is_Beginnest): Likewise.
+	(_Safe_iterator<>::_M_is_beginnest): Add.
+	* include/debug/safe_iterator.tcc (_Safe_iterator<>::_M_valid_range):
+	Use the latter.
+	* testsuite/23_containers/forward_list/debug/splice_after.cc:
+	Add test.
+
 2012-04-12  Benjamin Kosnik  <bkoz@redhat.com>
 
 	* include/bits/unordered_map.h (__unordered_map): Remove.
diff --git a/libstdc++-v3/include/debug/forward_list b/libstdc++-v3/include/debug/forward_list
index e21eb4a703a..f4a7ee96df0 100644
--- a/libstdc++-v3/include/debug/forward_list
+++ b/libstdc++-v3/include/debug/forward_list
@@ -760,8 +760,12 @@ namespace __gnu_debug
       typedef typename _It::iterator_type _BaseIt;
 
       static bool
-      _M_Is(_BaseIt __it, const _Sequence* __seq)
+      _S_Is(_BaseIt __it, const _Sequence* __seq)
       { return __it == __seq->_M_base().cbefore_begin(); }
+
+      static bool
+      _S_Is_Beginnest(_BaseIt __it, const _Sequence* __seq)
+      { return _S_Is(__it, __seq); }
     };
 }
 
diff --git a/libstdc++-v3/include/debug/safe_iterator.h b/libstdc++-v3/include/debug/safe_iterator.h
index b02fa7ab8ff..3cab2d7d8a2 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -50,8 +50,12 @@ namespace __gnu_debug
       typedef typename _It::iterator_type _BaseIt;
 
       static bool
-      _M_Is(_BaseIt __it, const _Sequence* __seq)
+      _S_Is(_BaseIt, const _Sequence*)
       { return false; }
+
+      static bool
+      _S_Is_Beginnest(_BaseIt __it, const _Sequence* __seq)
+      { return __it == __seq->_M_base().begin(); }
     };
 
   /** Iterators that derive from _Safe_iterator_base but that aren't
@@ -465,7 +469,15 @@ namespace __gnu_debug
       /// any?
       bool _M_is_before_begin() const
       {
-	return _BeforeBeginHelper<_Sequence>::_M_Is(base(), _M_get_sequence());
+	return _BeforeBeginHelper<_Sequence>::_S_Is(base(), _M_get_sequence());
+      }
+
+      /// Is this iterator equal to the sequence's before_begin() iterator if
+      /// any or begin() otherwise?
+      bool _M_is_beginnest() const
+      {
+	return _BeforeBeginHelper<_Sequence>::_S_Is_Beginnest(base(),
+							  _M_get_sequence());
       }
     };
 
diff --git a/libstdc++-v3/include/debug/safe_iterator.tcc b/libstdc++-v3/include/debug/safe_iterator.tcc
index 777a707e7f3..f01252bf6c2 100644
--- a/libstdc++-v3/include/debug/safe_iterator.tcc
+++ b/libstdc++-v3/include/debug/safe_iterator.tcc
@@ -1,6 +1,6 @@
 // Debugging iterator implementation (out of line) -*- C++ -*-
 
-// Copyright (C) 2003, 2004, 2005, 2006, 2007, 2009, 2010, 2011
+// Copyright (C) 2003, 2004, 2005, 2006, 2007, 2009, 2010, 2011, 2012
 // Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
@@ -91,10 +91,11 @@ namespace __gnu_debug
 	/* We can only test for equality, but check if one of the
 	   iterators is at an extreme. */
 	/* Optim for classic [begin, it) or [it, end) ranges, limit checks
-	 * when code is valid. */
-	if (_M_is_begin() || __rhs._M_is_end())
+	 * when code is valid.  Note, for the special case of forward_list,
+	 * before_begin replaces the role of begin.  */ 
+	if (_M_is_beginnest() || __rhs._M_is_end())
 	  return true;
-	if (_M_is_end() || __rhs._M_is_begin())
+	if (_M_is_end() || __rhs._M_is_beginnest())
 	  return false;
 
 	// Assume that this is a valid range; we can't check anything else
diff --git a/libstdc++-v3/testsuite/23_containers/forward_list/debug/splice_after.cc b/libstdc++-v3/testsuite/23_containers/forward_list/debug/splice_after.cc
index 60297551dcd..4cc1cfcf78d 100644
--- a/libstdc++-v3/testsuite/23_containers/forward_list/debug/splice_after.cc
+++ b/libstdc++-v3/testsuite/23_containers/forward_list/debug/splice_after.cc
@@ -1,6 +1,6 @@
 // { dg-options "-std=gnu++0x" }
 
-// Copyright (C) 2010 Free Software Foundation, Inc.
+// Copyright (C) 2010, 2012 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
@@ -34,6 +34,10 @@ test01()
 
   VERIFY( before == fl1.before_begin() );
   VERIFY( end == fl1.end() );
+
+  // no-op just to check that debug mode does not see any problem with it.
+  fl1.splice_after(fl1.before_begin(), std::move(fl2),
+		   fl2.before_begin(), fl2.begin());
 }
 
 int