diff --git a/configure b/configure
index 0a365941a..e59c53382 100755
--- a/configure
+++ b/configure
@@ -4141,10 +4141,25 @@ else
 #include "confdefs.h"
 #include <stdio.h>
 int main() {
-stdout->_fileno = 1
+stdout->__file = 1
 ; return 0; }
 EOF
 if { (eval echo configure:4148: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+  rm -rf conftest*
+  scm_cv_fd_setter="__file"
+else
+  echo "configure: failed program was:" >&5
+  cat conftest.$ac_ext >&5
+  rm -rf conftest*
+  cat > conftest.$ac_ext <<EOF
+#line 4156 "configure"
+#include "confdefs.h"
+#include <stdio.h>
+int main() {
+stdout->_fileno = 1
+; return 0; }
+EOF
+if { (eval echo configure:4163: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
   rm -rf conftest*
   scm_cv_fd_setter="_fileno"
 else
@@ -4157,6 +4172,8 @@ rm -f conftest*
 fi
 rm -f conftest*
 fi
+rm -f conftest*
+fi
 
 
 if test "$scm_cv_fd_setter"; then
@@ -4173,7 +4190,7 @@ fi
 # How to find out whether a FILE structure contains buffered data.
 # From Tk we have the following list:
 #		_cnt:		Most UNIX systems
-#		__cnt:		HPUX
+#		__cnt:		HPUX and SCO
 #		_r:		BSD
 #		readCount:	Sprite
 #	Or, in GNU libc there are two fields, _gptr and _egptr, which
@@ -4182,19 +4199,19 @@ fi
 #--------------------------------------------------------------------
 
 echo $ac_n "checking how to get buffer char count from FILE structure""... $ac_c" 1>&6
-echo "configure:4186: checking how to get buffer char count from FILE structure" >&5
+echo "configure:4203: checking how to get buffer char count from FILE structure" >&5
 if eval "test \"`echo '$''{'scm_cv_struct_file_count'+set}'`\" = set"; then
   echo $ac_n "(cached) $ac_c" 1>&6
 else
   cat > conftest.$ac_ext <<EOF
-#line 4191 "configure"
+#line 4208 "configure"
 #include "confdefs.h"
 #include <stdio.h>
 int main() {
 FILE *f = stdin; f->_cnt = 0
 ; return 0; }
 EOF
-if { (eval echo configure:4198: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+if { (eval echo configure:4215: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
   rm -rf conftest*
   scm_cv_struct_file_count="_cnt"
 else
@@ -4202,14 +4219,29 @@ else
   cat conftest.$ac_ext >&5
   rm -rf conftest*
   cat > conftest.$ac_ext <<EOF
-#line 4206 "configure"
+#line 4223 "configure"
+#include "confdefs.h"
+#include <stdio.h>
+int main() {
+FILE *f = stdin; f->__cnt = 0
+; return 0; }
+EOF
+if { (eval echo configure:4230: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+  rm -rf conftest*
+  scm_cv_struct_file_count="__cnt"
+else
+  echo "configure: failed program was:" >&5
+  cat conftest.$ac_ext >&5
+  rm -rf conftest*
+  cat > conftest.$ac_ext <<EOF
+#line 4238 "configure"
 #include "confdefs.h"
 #include <stdio.h>
 int main() {
 FILE *f = stdin; f->_r = 0
 ; return 0; }
 EOF
-if { (eval echo configure:4213: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+if { (eval echo configure:4245: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
   rm -rf conftest*
   scm_cv_struct_file_count="_r"
 else
@@ -4217,14 +4249,14 @@ else
   cat conftest.$ac_ext >&5
   rm -rf conftest*
   cat > conftest.$ac_ext <<EOF
-#line 4221 "configure"
+#line 4253 "configure"
 #include "confdefs.h"
 #include <stdio.h>
 int main() {
 FILE *f = stdin; f->readCount = 0
 ; return 0; }
 EOF
-if { (eval echo configure:4228: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+if { (eval echo configure:4260: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
   rm -rf conftest*
   scm_cv_struct_file_count="readCount"
 else
@@ -4239,6 +4271,8 @@ rm -f conftest*
 fi
 rm -f conftest*
 fi
+rm -f conftest*
+fi
 
 if test "$scm_cv_struct_file_count"; then
 	echo "$ac_t""$scm_cv_struct_file_count" 1>&6
@@ -4251,14 +4285,14 @@ if eval "test \"`echo '$''{'scm_cv_struct_file_gptr'+set}'`\" = set"; then
   echo $ac_n "(cached) $ac_c" 1>&6
 else
   cat > conftest.$ac_ext <<EOF
-#line 4255 "configure"
+#line 4289 "configure"
 #include "confdefs.h"
 #include <stdio.h>
 int main() {
 FILE *f = stdin; f->_gptr = f->egptr;
 ; return 0; }
 EOF
-if { (eval echo configure:4262: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+if { (eval echo configure:4296: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
   rm -rf conftest*
   scm_cv_struct_file_gptr=1
 else
@@ -4281,14 +4315,14 @@ if eval "test \"`echo '$''{'scm_cv_struct_file_readptr'+set}'`\" = set"; then
   echo $ac_n "(cached) $ac_c" 1>&6
 else
   cat > conftest.$ac_ext <<EOF
-#line 4285 "configure"
+#line 4319 "configure"
 #include "confdefs.h"
 #include <stdio.h>
 int main() {
 FILE *f = stdin; f->_IO_read_ptr = f->_IO_read_end;
 ; return 0; }
 EOF
-if { (eval echo configure:4292: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
+if { (eval echo configure:4326: \"$ac_compile\") 1>&5; (eval $ac_compile) 2>&5; }; then
   rm -rf conftest*
   scm_cv_struct_file_readptr=1
 else
@@ -4329,7 +4363,7 @@ fi
 ### Turn $with_threads into either the name of a threads package, like
 ### `qt', or `no', meaning that threads should not be supported.
 echo $ac_n "checking whether to support threads""... $ac_c" 1>&6
-echo "configure:4333: checking whether to support threads" >&5
+echo "configure:4367: checking whether to support threads" >&5
 case "$with_threads" in
   "yes" | "qt" | "coop" | "")
     with_threads=qt
@@ -4353,7 +4387,7 @@ case "${with_threads}" in
   
 
   echo $ac_n "checking QuickThreads configuration""... $ac_c" 1>&6
-echo "configure:4357: checking QuickThreads configuration" >&5
+echo "configure:4391: checking QuickThreads configuration" >&5
   # How can we refer to the qt source directory from within the qt build
   # directory?  For headers, we can rely on the fact that the qt src
   # directory appears in the #include path.
@@ -4484,7 +4518,7 @@ do
 # Extract the first word of "$ac_prog", so it can be a program name with args.
 set dummy $ac_prog; ac_word=$2
 echo $ac_n "checking for $ac_word""... $ac_c" 1>&6
-echo "configure:4488: checking for $ac_word" >&5
+echo "configure:4522: checking for $ac_word" >&5
 if eval "test \"`echo '$''{'ac_cv_prog_AWK'+set}'`\" = set"; then
   echo $ac_n "(cached) $ac_c" 1>&6
 else
diff --git a/configure.in b/configure.in
index f47626bd1..1d90409c7 100644
--- a/configure.in
+++ b/configure.in
@@ -255,10 +255,13 @@ AC_CACHE_VAL(scm_cv_fd_setter,
 	AC_TRY_COMPILE([#include <stdio.h>],
 			[stdout->_file = 1],
 			scm_cv_fd_setter="_file",
+	AC_TRY_COMPILE([#include <stdio.h>],
+			[stdout->__file = 1],
+			scm_cv_fd_setter="__file",
 	AC_TRY_COMPILE([#include <stdio.h>],
 			[stdout->_fileno = 1],
 			scm_cv_fd_setter="_fileno",
-			scm_cv_fd_setter="")))
+			scm_cv_fd_setter=""))))
 
 if test "$scm_cv_fd_setter"; then
 	AC_MSG_RESULT($scm_cv_fd_setter)
@@ -271,7 +274,7 @@ fi
 # How to find out whether a FILE structure contains buffered data.
 # From Tk we have the following list:
 #		_cnt:		Most UNIX systems
-#		__cnt:		HPUX
+#		__cnt:		HPUX and SCO
 #		_r:		BSD
 #		readCount:	Sprite
 #	Or, in GNU libc there are two fields, _gptr and _egptr, which
@@ -284,13 +287,16 @@ AC_CACHE_VAL(scm_cv_struct_file_count,
 	AC_TRY_COMPILE([#include <stdio.h>],
 			[FILE *f = stdin; f->_cnt = 0],
 			scm_cv_struct_file_count="_cnt",
+	AC_TRY_COMPILE([#include <stdio.h>],
+			[FILE *f = stdin; f->__cnt = 0],
+			scm_cv_struct_file_count="__cnt",
 	AC_TRY_COMPILE([#include <stdio.h>],
 			[FILE *f = stdin; f->_r = 0],
 			scm_cv_struct_file_count="_r",
 	AC_TRY_COMPILE([#include <stdio.h>],
 			[FILE *f = stdin; f->readCount = 0],
 			scm_cv_struct_file_count="readCount",
-	scm_cv_struct_file_count=""))))
+	scm_cv_struct_file_count="")))))
 if test "$scm_cv_struct_file_count"; then
 	AC_MSG_RESULT($scm_cv_struct_file_count)
 	AC_DEFINE_UNQUOTED(FILE_CNT_FIELD, $scm_cv_struct_file_count)