diff --git a/configure.ac b/configure.ac
index 99779dc..1cd8b22 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,7 +32,7 @@ CPPFLAGS="$CPPFLAGS -I$S48DIR/include"
 # Checks for libraries.
 
 # Checks for header files.
-AC_CHECK_HEADERS([fcntl.h limits.h netdb.h sgtty.h stdlib.h string.h sys/ioctl.h sys/param.h sys/time.h termios.h unistd.h utime.h])
+AC_CHECK_HEADERS([fcntl.h limits.h netdb.h pty.h sgtty.h stdlib.h string.h sys/ioctl.h sys/param.h sys/time.h termios.h unistd.h utime.h])
 
 dnl  We need the scheme48.h headers, so bomb out if we can't find them.
 AC_CHECK_HEADERS([scheme48.h], [],