diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4561dba458af..027769555481 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2008-01-06  Paolo Carlini  <pcarlini@suse.de>
+
+	PR libstdc++/34680
+	* c-cppbuiltin.c (c_cpp_builtins): Define __GXX_RTTI, if appropriate.
+	* doc/cpp.texi ([Common Predefined Macros]): Document.
+
 2008-01-06  Uros Bizjak  <ubizjak@gmail.com>
 
 	* config/i386/i386.c (ix86_emit_swsqrtsf): Use negative constants in
diff --git a/gcc/c-cppbuiltin.c b/gcc/c-cppbuiltin.c
index e201b058f5f2..86c3f9cfff25 100644
--- a/gcc/c-cppbuiltin.c
+++ b/gcc/c-cppbuiltin.c
@@ -449,6 +449,8 @@ c_cpp_builtins (cpp_reader *pfile)
 	cpp_define (pfile, "__GXX_WEAK__=0");
       if (warn_deprecated)
 	cpp_define (pfile, "__DEPRECATED");
+      if (flag_rtti)
+	cpp_define (pfile, "__GXX_RTTI");
       if (cxx_dialect == cxx0x)
         cpp_define (pfile, "__GXX_EXPERIMENTAL_CXX0X__");
     }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d66912b2ac2a..0a0db6b7b657 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2008-01-06  Paolo Carlini  <pcarlini@suse.de>
+
+	PR libstdc++/34680
+	* g++.dg/rtti/predefined-rtti-macro-1.C: New.
+	* g++.dg/rtti/predefined-rtti-macro-2.C: Likewise.
+
 2008-01-06  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/34545
diff --git a/gcc/testsuite/g++.dg/rtti/predefined-rtti-macro-1.C b/gcc/testsuite/g++.dg/rtti/predefined-rtti-macro-1.C
new file mode 100644
index 000000000000..5c94bc1de177
--- /dev/null
+++ b/gcc/testsuite/g++.dg/rtti/predefined-rtti-macro-1.C
@@ -0,0 +1,12 @@
+// { dg-do compile }
+
+struct A { virtual ~A() { }; };
+struct B : A { };
+
+void f(B* bp)
+{
+  bp =
+#ifdef __GXX_RTTI
+  dynamic_cast<B*>(static_cast<A*>(0));
+#endif
+}
diff --git a/gcc/testsuite/g++.dg/rtti/predefined-rtti-macro-2.C b/gcc/testsuite/g++.dg/rtti/predefined-rtti-macro-2.C
new file mode 100644
index 000000000000..284f2f64a23b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/rtti/predefined-rtti-macro-2.C
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// { dg-options "-fno-rtti" }
+
+struct B { };
+
+void f(B* bp)
+{
+  bp =
+#ifndef __GXX_RTTI
+  static_cast<B*>(0);
+#endif
+}