--- a/configure.in
+++ b/configure.in
@@ -1,6 +1,12 @@
 dnl Process this file with autoconf to produce a configure script.
 dnl
 AC_INIT([[src]]/octave.cc)dnl
+AC_CONFIG_HEADER(config.h)dnl
+
+root_srcdir=$srcdir
+AC_SUBST(root_srcdir)dnl
+
+AC_DEFINE(OCTAVE_SOURCE, 1)dnl
 
 # See if we were given the target host type.  If not, guess.
 
@@ -45,7 +51,7 @@
   DLD_DIR=dld
   LIBDLD='../libdld.a'
   DLD_OBJECTS= : # don't link them in if doing dynamic linking
-  DEFS="$DEFS -DWITH_DLD=1"
+  AC_DEFINE(WITH_DLD, 1)dnl
   LD_STATIC_FLAG=-static
 fi
 AC_SUBST(DYNAMIC_LD_OBJ)dnl
@@ -58,21 +64,21 @@
 if test -f $srcdir/libcruft/npsol/npsol.f; then
   :
 else
-  DEFS="$DEFS -DNPSOL_MISSING=1"
+  AC_DEFINE(NPSOL_MISSING, 1)dnl
 fi
 
 echo "checking for qpsol"
 if test -f $srcdir/libcruft/qpsol/qpsol.f; then
   :
 else
-  DEFS="$DEFS -DQPSOL_MISSING=1"
+  AC_DEFINE(QPSOL_MISSING, 1)dnl
 fi
 
 echo "checking for fsqp"
 if test -f $srcdir/libcruft/fsqp/fsqpd.f; then
   :
 else
-  DEFS="$DEFS -DFSQP_MISSING=1"
+  AC_DEFINE(FSQP_MISSING, 1)dnl
 fi
 
 AC_PROG_CC
@@ -124,6 +130,10 @@
          you should probably consider getting version 2.x
 EOF
       ;;
+    2.5.*|2.6.*|2.7.*|2.8.*|2.9.*)
+      CXXFLAGS="$CXXFLAGS -fexternal-templates"
+      AC_DEFINE(USE_EXTERNAL_TEMPLATES, 1)dnl
+      ;;
     esac
 else
   cat << EOF
@@ -162,7 +172,7 @@
     status=$?
     if test $status -eq 0; then
       if test "$tmpdef" = '-DF77_APPEND_UNDERSCORE=1'; then
-        DEFS="$DEFS $tmpdef"
+        AC_DEFINE(F77_APPEND_UNDERSCORE, 1)dnl
       fi
     else
       F77=
@@ -210,7 +220,7 @@
 \%.c : \%.f\
 	cat $< | $(F2C) $(F2CFLAGS) > $(@F)'
   DEFAULT_DOT_O_FROM_DOT_F='\%.o : \%.f'
-  DEFS="$DEFS -DF77_APPEND_UNDERSCORE=1"
+  AC_DEFINE(F77_APPEND_UNDERSCORE, 1)dnl
 else
   cat << EOF
 warning: in order to build octave, you must have a compatible
@@ -293,9 +303,9 @@
 esac
 AC_SUBST(VOID_SIGHANDLER)dnl
 
-AC_HEADER_CHECK(termios.h, DEFS="$DEFS -DHAVE_TERMIOS_H=1",
-  AC_HEADER_CHECK(termio.h, DEFS="$DEFS -DHAVE_TERMIO_H=1",
-    AC_HEADER_CHECK(sgtty.h, DEFS="$DEFS -DHAVE_SGTTY_H=1", [])))dnl
+AC_HEADER_CHECK(termios.h, AC_DEFINE(HAVE_TERMIOS_H, 1),
+  AC_HEADER_CHECK(termio.h, AC_DEFINE(HAVE_TERMIO_H, 1),
+    AC_HEADER_CHECK(sgtty.h, AC_DEFINE(HAVE_SGTTY_H, 1), [])))dnl
 case "$DEFS" in
   *HAVE_TERMIOS_H* | *HAVE_TERMIO_H* | *HAVE_SGTTY_H*)
   ;;
@@ -335,13 +345,13 @@
   do
     case "$func" in
       *acosh.o*)
-	DEFS="$DEFS -DACOSH_MISSING=1"
+	AC_DEFINE(ACOSH_MISSING, 1)dnl
 	;;
       *asinh.o*)
-	DEFS="$DEFS -DASINH_MISSING=1"
+	AC_DEFINE(ASINH_MISSING, 1)dnl
 	;;
       *atanh.o*)
-	DEFS="$DEFS -DATANH_MISSING=1"
+	AC_DEFINE(ATANH_MISSING, 1)dnl
 	;;
     esac
   done
@@ -407,6 +417,9 @@
 fi
 AC_SUBST(RUNTEST)dnl
 
+UGLY_DEFS="$DEFS"
+AC_SUBST(UGLY_DEFS)dnl
+
 define([tmpa], [libcruft/blas/Makefile libcruft/balgen/Makefile])dnl
 define([tmpb], [libcruft/dassl/Makefile libcruft/eispack/Makefile])dnl
 define([tmpc], [libcruft/fftpack/Makefile libcruft/fsqp/Makefile])dnl