diff --git a/ChangeLog b/ChangeLog
index 759012fd..8f1368fb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2003-11-05  Hrvoje Niksic  <hniksic@xemacs.org>
+
+	* configure.in: Substitute ANSI2KNR and U, so we can compile.
+
 2003-11-05  Hrvoje Niksic  <hniksic@xemacs.org>
 
 	* configure.in: Use the Autoconf macro AC_C_PROTOTYPES instead of
diff --git a/configure.in b/configure.in
index 6d788311..be88f48f 100644
--- a/configure.in
+++ b/configure.in
@@ -109,12 +109,16 @@ test -z "$CFLAGS"  && CFLAGS= auto_cflags=1
 test -z "$CC" && cc_specified=yes
 
 AC_PROG_CC
+AC_AIX
+AM_PROG_CC_STDC
 
+dnl Turn on optimization by default.  Specifically:
 dnl
 dnl if the user hasn't specified CFLAGS, then
-dnl   if compiler is gcc, then use -O2 and some warning flags
-dnl   else use os-specific flags or -O
-dnl
+dnl   if compiler is gcc, then
+dnl     use -O2 and some warning flags
+dnl   else
+dnl     use os-specific flags or -O
 if test -n "$auto_cflags"; then
   if test -n "$GCC"; then
     CFLAGS="$CFLAGS -O2 -Wall -Wno-implicit"
@@ -127,11 +131,6 @@ if test -n "$auto_cflags"; then
   fi
 fi
 
-dnl
-dnl Handle AIX
-dnl
-AC_AIX
-
 dnl
 dnl Configure our included libtool and make sure it's regenerated when needed
 dnl
@@ -157,8 +156,17 @@ AC_C_VOLATILE
 AC_C_BIGENDIAN
 AC_C_PROTOTYPES
 
+if test x"$am_cv_prog_cc_stdc" != xno; then
+  true
+  AC_SUBST(U, [])
+  AC_SUBST(ANSI2KNR, [])
+else
+  AC_SUBST(U, [_])
+  AC_SUBST(ANSI2KNR, [./ansi2knr])
+fi
+
 dnl
-dnl Checks for headers that might be missing.
+dnl Checks for header files that might be missing.
 dnl
 
 dnl Check for basic headers, even those we assume the presence of.