diff --git a/ChangeLog b/ChangeLog
index 3e7aa70c6f..22c9df1ea3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed May 19 23:36:57 2010  Hidetoshi NAGAI  <nagai@ai.kyutech.ac.jp>
+
+	* ext/tk/extconf.rb: invalid result on searching tcl.h/tk.h.
+	  [ruby-def:41334] [Bug #3307]. Thanks, Masaya Tarui.
+
 Wed May 19 23:19:30 2010  Shugo Maeda  <shugo@ruby-lang.org>
 
 	* lib/net/imap.rb (disconnect): closes the socket of a Net::IMAP
diff --git a/ext/tk/extconf.rb b/ext/tk/extconf.rb
index 5b2878b30d..c5dbfeafa6 100644
--- a/ext/tk/extconf.rb
+++ b/ext/tk/extconf.rb
@@ -1,6 +1,6 @@
 ##############################################################
 # extconf.rb for tcltklib
-# release date: 2010-05-07
+# release date: 2010-05-19
 ##############################################################
 require 'mkmf'
 
@@ -989,7 +989,7 @@ def find_tcltk_header(tclver, tkver)
   end
 
   if TclConfig_Info['TCL_INCLUDE_SPEC'] && 
-      have_tcl_h = try_cpp('tcl.h', TclConfig_Info['TCL_INCLUDE_SPEC'])
+      have_tcl_h = try_cpp('#include <tcl.h>', TclConfig_Info['TCL_INCLUDE_SPEC'])
     $INCFLAGS << " " << TclConfig_Info['TCL_INCLUDE_SPEC']
   elsif have_tcl_h = have_header('tcl.h')
     # find
@@ -1009,7 +1009,7 @@ def find_tcltk_header(tclver, tkver)
   end
 
   if TkConfig_Info['TK_INCLUDE_SPEC'] && 
-      have_tk_h = try_cpp('tk.h', TkConfig_Info['TK_INCLUDE_SPEC'])
+      have_tk_h = try_cpp('#include <tk.h>', TkConfig_Info['TK_INCLUDE_SPEC'])
     $INCFLAGS << " " << TkConfig_Info['TK_INCLUDE_SPEC']
   elsif have_tk_h = have_header('tk.h')
     # find