diff --git a/ChangeLog b/ChangeLog
index 9188d535..79bdeb01 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2005-08-10  Peter Ekberg  <peda@lysator.liu.se>
+
+	* m4/libtool.m4 (_LT_LANG_CXX_CONFIG): Set ac_ext to cpp, not cc.
+
 2005-08-08  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
 
 	* config/ltmain.m4sh (inherited_linker_flags): Backed out broken
diff --git a/m4/libtool.m4 b/m4/libtool.m4
index b0b1c734..522f103c 100644
--- a/m4/libtool.m4
+++ b/m4/libtool.m4
@@ -4744,7 +4744,7 @@ _LT_TAGVAR(whole_archive_flag_spec, $1)=
 _LT_TAGVAR(enable_shared_with_static_runtimes, $1)=no
 
 # Source file extension for C++ test sources.
-ac_ext=cc
+ac_ext=cpp
 
 # Object file extension for compiled C++ test sources.
 objext=o