diff --git a/ChangeLog b/ChangeLog
index 7a2730496..db2a7ce03 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2011-12-16  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Don't rely on the g++ version to include tr1/unordered_map and co.
+
+	The previous setup failed with clang++ 3.0.
+
+	* m4/stl.m4: New file.
+	* configure.ac: Call AC_HEADER_UNORDERED_MAP,
+	AC_HEADER_TR1_UNORDERED_MAP, and AC_HEADER_EXT_HASH_MAP.
+	* src/misc/hash.hh: Include _config.h, and used the
+	SPOT_HAVE_UNORDERED_MAP, SPOT_HAVE_TR1_UNORDERED_MAP,
+	or SPOT_HAVE_EXT_HASH_MAP defines to decide which
+	file to include.
+
 2011-12-01  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	Fix mkdir error in ajax/spot.in.
@@ -4331,7 +4345,7 @@
 
 	Update to compile with the Intel compiler.
 
-  	* m4/intel.m4: New file.
+	* m4/intel.m4: New file.
 	* configure.ac: Update.
 	* src/tgbaalgos/emptiness.cc (tgba_run): Modify s.s->clone() in
 	i->s->clone().
diff --git a/configure.ac b/configure.ac
index 5cdefd619..746a2399a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -46,6 +46,10 @@ AC_PROG_YACC
 
 AC_LANG(C++)
 
+AC_HEADER_UNORDERED_MAP
+AC_HEADER_TR1_UNORDERED_MAP
+AC_HEADER_EXT_HASH_MAP
+
 AX_CHECK_BUDDY
 AX_CHECK_LBTT
 AX_CHECK_GSPNLIB
diff --git a/m4/stl.m4 b/m4/stl.m4
new file mode 100644
index 000000000..439630edd
--- /dev/null
+++ b/m4/stl.m4
@@ -0,0 +1,51 @@
+
+AC_DEFUN([AC_HEADER_EXT_HASH_MAP], [
+  AC_CACHE_CHECK([for ext/hash_map],
+  [ac_cv_cxx_ext_hash_map],
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -Werror"
+  AC_TRY_COMPILE([#include <ext/hash_map>], [using __gnu_cxx::hash_map;],
+  [ac_cv_cxx_ext_hash_map=yes], [ac_cv_cxx_ext_hash_map=no])
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  AC_LANG_RESTORE
+  ])
+  if test "$ac_cv_cxx_ext_hash_map" = yes; then
+    AC_DEFINE([HAVE_EXT_HASH_MAP],, [Define if ext/hash_map is present.])
+  fi
+])
+
+AC_DEFUN([AC_HEADER_TR1_UNORDERED_MAP], [
+  AC_CACHE_CHECK([for tr1/unordered_map],
+  [ac_cv_cxx_tr1_unordered_map],
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -Werror"
+  AC_TRY_COMPILE([#include <tr1/unordered_map>], [using std::tr1::unordered_map;],
+  [ac_cv_cxx_tr1_unordered_map=yes], [ac_cv_cxx_tr1_unordered_map=no])
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  AC_LANG_RESTORE
+  ])
+  if test "$ac_cv_cxx_tr1_unordered_map" = yes; then
+    AC_DEFINE([HAVE_TR1_UNORDERED_MAP],, [Define if tr1/unordered_map is present.])
+  fi
+])
+
+AC_DEFUN([AC_HEADER_UNORDERED_MAP], [
+  AC_CACHE_CHECK([for unordered_map],
+  [ac_cv_cxx_unordered_map],
+  [AC_LANG_SAVE
+  AC_LANG_CPLUSPLUS
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -Werror"
+  AC_TRY_COMPILE([#include <unordered_map>], [using std::unordered_map;],
+  [ac_cv_cxx_unordered_map=yes], [ac_cv_cxx_unordered_map=no])
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  AC_LANG_RESTORE
+  ])
+  if test "$ac_cv_cxx_unordered_map" = yes; then
+    AC_DEFINE([HAVE_UNORDERED_MAP],, [Define if unordered_map is present.])
+  fi
+])
diff --git a/src/misc/hash.hh b/src/misc/hash.hh
index f13a4fc72..9d2dde9be 100644
--- a/src/misc/hash.hh
+++ b/src/misc/hash.hh
@@ -26,11 +26,35 @@
 
 #  include <string>
 #  include <functional>
-#  include "hashfunc.hh"
+#  include "misc/hashfunc.hh"
+#  include "misc/_config.h"
 
-// See the G++ FAQ for details about the following.
-#  ifdef __GNUC__
-#  if __GNUC__ < 3
+#ifdef SPOT_HAVE_UNORDERED_MAP
+#  include <unordered_map>
+#  include <unordered_set>
+   namespace Sgi = std;
+#  define hash_map unordered_map
+#  define hash_multimap unordered_multimap
+#  define hash_set unordered_set
+#else
+#ifdef SPOT_HAVE_TR1_UNORDERED_MAP
+#  include <tr1/unordered_map>
+#  include <tr1/unordered_set>
+   namespace Sgi = std::tr1;
+#  define hash_map unordered_map
+#  define hash_multimap unordered_multimap
+#  define hash_set unordered_set
+#else
+#ifdef SPOT_HAVE_EXT_HASH_MAP
+#  include <ext/hash_map>
+#  include <ext/hash_set>
+#  if __GNUC__ == 3 && __GNUC_MINOR__ == 0
+     namespace Sgi = std;               // GCC 3.0
+#  else
+     namespace Sgi = ::__gnu_cxx;       // GCC 3.1 to 4.2
+#  endif
+#else
+#  if defined(__GNUC__) && (__GNUC__ < 3)
 #    include <hash_map.h>
 #    include <hash_set.h>
     namespace Sgi
@@ -41,28 +65,13 @@
       using ::hash;
     }
 #  else
-#    if (__GNUC__ == 4 && __GNUC_MINOR__ >= 3) || __GNUC__ > 4
-#      include <tr1/unordered_set>         // GCC 4.3
-#      include <tr1/unordered_map>
-       namespace Sgi = std::tr1;
-#      define hash_map unordered_map
-#      define hash_multimap unordered_multimap
-#      define hash_set unordered_set
-#    else
-#      include <ext/hash_map>
-#      include <ext/hash_set>
-#      if __GNUC__ == 3 && __GNUC_MINOR__ == 0
-        namespace Sgi = std;               // GCC 3.0
-#      else
-        namespace Sgi = ::__gnu_cxx;       // GCC 3.1 to 4.2
-#      endif
-#    endif
-#  endif
-#  else      // ...  there are other compilers, right?
 #   include <hash_map>
 #   include <hash_set>
     namespace Sgi = std;
 #  endif
+#endif
+#endif
+#endif
 
 namespace spot
 {
@@ -83,9 +92,9 @@ namespace spot
   /// \brief A hash function for strings.
   /// \ingroup hash_funcs
   /// @{
-#  if (__GNUC__ == 4 && __GNUC_MINOR__ >= 3) || __GNUC__ > 4
-  typedef std::tr1::hash<std::string> string_hash;
-#  else  // GCC < 4.3
+#if defined(SPOT_HAVE_UNORDERED_MAP) || defined(SPOT_HAVE_TR1_UNORDERED_MAP)
+  typedef Sgi::hash<std::string> string_hash;
+#else // e.g. GCC < 4.3
   struct string_hash:
     public Sgi::hash<const char*>,
     public std::unary_function<const std::string&, size_t>
@@ -98,7 +107,7 @@ namespace spot
     }
   };
   /// @}
-#  endif
+#endif
 
   /// \brief A hash function that returns identity
   /// \ingroup hash_funcs