diff --git a/configure.ac b/configure.ac
index 63bd5b8..bee33f0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -63,24 +63,7 @@ dnl FIXME
 AC_CHECK_HEADERS(unistd.h)
 
 # If the FIONREAD ioctl command is defined, which file must be included?
-AC_MSG_CHECKING(for FIONREAD in termios.h)
-AC_EGREP_HEADER(FIONREAD, termios.h, [
-  AC_MSG_RESULT(yes) AC_DEFINE(FIONREAD_IN_TERMIOS_H, 1, Define if <termios.h> defines FIONREAD)
-],[
-  AC_MSG_RESULT(no)
-  AC_MSG_CHECKING(for FIONREAD in sys/ioctl.h)
-  AC_EGREP_HEADER(FIONREAD, sys/ioctl.h, [
-    AC_MSG_RESULT(yes) AC_DEFINE(FIONREAD_IN_SYS_IOCTL_H, 1, Define if <sys/ioctl.h> defines FIONREAD)
-  ],[
-    AC_MSG_RESULT(no)
-    AC_MSG_CHECKING(for FIONREAD in sys/filio.h)
-    AC_EGREP_HEADER(FIONREAD, sys/filio.h, [
-      AC_MSG_RESULT(yes) AC_DEFINE(FIONREAD_IN_SYS_FILIO_H, 1, Define if <sys/filio.h> defines FIONREAD)
-    ],[
-      AC_MSG_RESULT(no)
-    ])
-  ])
-])
+AC_CHECK_HEADERS(termios.h sys/ioctl.h sys/filio.h)
 
 # If getdtablesize() is available to determine the maximum number of open
 # files per process, set getdtablesize=yes.
@@ -249,16 +232,22 @@ AC_DEFINE(TERMIO, 1, [FIXME HARD])
 #    tiocflush   use TIOCFLUSH ioctl from <sys/ioctl.h>
 #    tcflsh      use TCFLSH ioctl from <termio.h>
 # Leave the variable(s) empty if flushing is not supported.
-if false; then
-  AC_DEFINE(FLUSH_BSD, 1, [FIXME HARD])
+AC_CHECK_FUNCS(fpurge)
+
+AC_CACHE_CHECK([for BSD-style flushing],
+  [ac_cv_have_bsd_flush],
+  [AC_TRY_COMPILE(
+    [#include <stdio.h>],
+    [FILE *f;
+     f->_cnt = 0;
+     f->_ptr = f->_base;],
+    ac_cv_have_bsd_flush=yes,
+    ac_cv_have_bsd_flush=no)])
+if test "${ac_cv_have_bsd_flush}" = "yes"; then
+  AC_DEFINE(HAVE_BSD_FLUSH, 1, [Define if you have BSD-style flushing])
 fi
-if false; then
-  AC_DEFINE(FLUSH_FPURGE, 1, [FIXME HARD])
-fi
-if false; then
-  AC_DEFINE(FLUSH_TIOCFLUSH, 1, [FIXME HARD])
-fi
-AC_DEFINE(FLUSH_TCFLSH, 1, [FIXME HARD])
+
+AC_CHECK_HEADERS(termio.h termios.h)
 
 # The interpreter uses the getrlimit function to determine the maximum
 # stack size of the running program.  If this function is not supported,
diff --git a/src/print.c b/src/print.c
index a57e341..9fbfd8d 100644
--- a/src/print.c
+++ b/src/print.c
@@ -35,12 +35,14 @@
 #include <ctype.h>
 #include <stdarg.h>
 
-#ifdef FLUSH_TIOCFLUSH
-#  include <sys/ioctl.h>
-#else
-#ifdef FLUSH_TCFLSH
-#  include <termio.h>
+#if defined(HAVE_TERMIO_H)
+#   include <termio.h>
+#elif defined(HAVE_TERMIOS_H)
+#   include <termios.h>
 #endif
+
+#if defined(HAVE_SYS_IOCTL_H)
+#   include <sys/ioctl.h>
 #endif
 
 #include "kernel.h"
@@ -203,21 +205,18 @@ void Discard_Output (Object port) {
     if (PORT(port)->flags & P_STRING)
         return;
     f = PORT(port)->file;
-#ifdef FLUSH_FPURGE
+#if defined(HAVE_FPURGE)
     (void)fpurge (f);
-#else
-#ifdef FLUSH_BSD
+#elif defined(HAVE_BSD_FLUSH)
     f->_cnt = 0;
     f->_ptr = f->_base;
 #endif
-#endif
-#ifdef FLUSH_TIOCFLUSH
+
+#if defined(TIOCFLUSH)
     (void)ioctl (fileno (f), TIOCFLUSH, (char *)0);
-#else
-#ifdef FLUSH_TCFLSH
+#elif defined(TCFLSH)
     (void)ioctl (fileno (f), TCFLSH, (char *)1);
 #endif
-#endif
 }
 
 Object P_Flush_Output_Port (int argc, Object *argv) {
diff --git a/src/read.c b/src/read.c
index ceb13e0..8714664 100644
--- a/src/read.c
+++ b/src/read.c
@@ -34,19 +34,17 @@
 #include <limits.h>
 #include <string.h>
 
-#ifdef FLUSH_TIOCFLUSH
-#  include <sys/ioctl.h>
-#else
-#ifdef FLUSH_TCFLSH
-#  include <termio.h>
-#endif
+#if defined(HAVE_TERMIO_H)
+#   include <termio.h>
+#elif defined(HAVE_TERMIOS_H)
+#   include <termios.h>
 #endif
 
-#if defined(FIONREAD_IN_TERMIOS_H)
-#   include <termios.h>
-#elif defined(FIONREAD_IN_SYS_IOCTL_H)
+#if defined(HAVE_SYS_IOCTL_H)
 #   include <sys/ioctl.h>
-#elif defined(FIONREAD_IN_SYS_FILIO_H)
+#endif
+
+#if defined(HAVE_SYS_FILIO_H)
 #   include <sys/filio.h>
 #endif
 
@@ -146,21 +144,18 @@ void Discard_Input (Object port) {
     if (PORT(port)->flags & P_STRING)
         return;
     f = PORT(port)->file;
-#ifdef FLUSH_FPURGE
+#if defined(HAVE_FPURGE)
     (void)fpurge (f);
-#else
-#ifdef FLUSH_BSD
+#elif defined(HAVE_BSD_FLUSH)
     f->_cnt = 0;
     f->_ptr = f->_base;
 #endif
-#endif
-#ifdef FLUSH_TIOCFLUSH
+
+#if defined(TIOCFLUSH)
     (void)ioctl (fileno (f), TIOCFLUSH, (char *)0);
-#else
-#ifdef FLUSH_TCFLSH
+#elif defined(TCFLSH)
     (void)ioctl (fileno (f), TCFLSH, (char *)0);
 #endif
-#endif
 }
 
 Object P_Unread_Char (int argc, Object *argv) {