diff --git a/configure b/configure
index 0f74a29274e..3e280b312ef 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 1.429 .
+# From configure.in Revision: 1.430 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.57 for python 2.4.
 #
@@ -17520,6 +17520,58 @@ _ACEOF
 
 fi
 
+echo "$as_me:$LINENO: checking for UCS-4 tcl" >&5
+echo $ECHO_N "checking for UCS-4 tcl... $ECHO_C" >&6
+have_ucs4_tcl=no
+cat >conftest.$ac_ext <<_ACEOF
+#line $LINENO "configure"
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+#include <tcl.h>
+#if TCL_UTF_MAX != 6
+# error "NOT UCS4_TCL"
+#endif
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
+  (eval $ac_compile) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+         { ac_try='test -s conftest.$ac_objext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+
+
+cat >>confdefs.h <<\_ACEOF
+#define HAVE_UCS4_TCL 1
+_ACEOF
+
+  have_ucs4_tcl=yes
+
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+fi
+rm -f conftest.$ac_objext conftest.$ac_ext
+echo "$as_me:$LINENO: result: $have_ucs4_tcl" >&5
+echo "${ECHO_T}$have_ucs4_tcl" >&6
+
 echo "$as_me:$LINENO: checking what type to use for unicode" >&5
 echo $ECHO_N "checking what type to use for unicode... $ECHO_C" >&6
 # Check whether --enable-unicode or --disable-unicode was given.
@@ -17533,7 +17585,12 @@ fi;
 if test $enable_unicode = yes
 then
   # Without any arguments, Py_UNICODE defaults to two-byte mode
-  enable_unicode="ucs2"
+  case "$have_ucs4_tcl" in
+  yes) enable_unicode="ucs4"
+       ;;
+  *)   enable_unicode="ucs2"
+       ;;
+  esac
 fi
 
 
diff --git a/configure.in b/configure.in
index 44da831c852..70e1ff94642 100644
--- a/configure.in
+++ b/configure.in
@@ -2647,6 +2647,18 @@ then
   AC_CHECK_SIZEOF(wchar_t, 4, [#include <wchar.h>])
 fi
 
+AC_MSG_CHECKING(for UCS-4 tcl)
+have_ucs4_tcl=no
+AC_TRY_COMPILE([
+#include <tcl.h>
+#if TCL_UTF_MAX != 6
+# error "NOT UCS4_TCL"
+#endif], [], [
+  AC_DEFINE(HAVE_UCS4_TCL, 1, [Define this if you have tcl and TCL_UTF_MAX==6])
+  have_ucs4_tcl=yes
+])
+AC_MSG_RESULT($have_ucs4_tcl)
+
 AC_MSG_CHECKING(what type to use for unicode)
 dnl quadrigraphs "@<:@" and "@:>@" produce "[" and "]" in the output
 AC_ARG_ENABLE(unicode, 
@@ -2657,7 +2669,12 @@ AC_ARG_ENABLE(unicode,
 if test $enable_unicode = yes
 then
   # Without any arguments, Py_UNICODE defaults to two-byte mode
-  enable_unicode="ucs2"
+  case "$have_ucs4_tcl" in
+  yes) enable_unicode="ucs4"
+       ;;
+  *)   enable_unicode="ucs2"
+       ;;
+  esac
 fi
 
 AH_TEMPLATE(Py_UNICODE_SIZE,