diff --git a/compat.h b/compat.h
index 2b666b1f..d38e6f0c 100644
--- a/compat.h
+++ b/compat.h
@@ -18,6 +18,7 @@
 #define COMPAT_H
 
 #include <sys/types.h>
+#include <sys/ioctl.h>
 #include <sys/uio.h>
 
 #include <limits.h>
@@ -283,9 +284,15 @@ int		 b64_ntop(const char *, size_t, char *, size_t);
 int		 b64_pton(const char *, u_char *, size_t);
 #endif
 
+#ifndef HAVE_FDFORKPTY
+/* fdforkpty.c */
+int		 getptmfd(void);
+pid_t		 fdforkpty(int, int *, char *, struct termios *,
+		     struct winsize *);
+#endif
+
 #ifndef HAVE_FORKPTY
 /* forkpty.c */
-#include <sys/ioctl.h>
 pid_t		 forkpty(int *, char *, struct termios *, struct winsize *);
 #endif
 
diff --git a/compat/fdforkpty.c b/compat/fdforkpty.c
new file mode 100644
index 00000000..c05f0dbf
--- /dev/null
+++ b/compat/fdforkpty.c
@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2017 Nicholas Marriott <nicholas.marriott@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+
+#include <limits.h>
+
+#include "compat.h"
+
+int
+getptmfd(void)
+{
+	return (INT_MAX);
+}
+
+pid_t
+fdforkpty(__unused int ptmfd, int *master, char *name, struct termios *tio,
+    struct winsize *ws)
+{
+	return (forkpty(master, name, tio, ws));
+}
diff --git a/compat/forkpty-aix.c b/compat/forkpty-aix.c
index 31b084db..5eba9fd6 100644
--- a/compat/forkpty-aix.c
+++ b/compat/forkpty-aix.c
@@ -29,7 +29,8 @@ void fatal(const char *, ...);
 void fatalx(const char *, ...);
 
 pid_t
-forkpty(int *master, unused char *name, struct termios *tio, struct winsize *ws)
+forkpty(int *master, __unused char *name, struct termios *tio,
+    struct winsize *ws)
 {
 	int	slave = -1, fd, pipe_fd[2];
 	char   *path, dummy;
diff --git a/compat/setenv.c b/compat/setenv.c
index 9f9295c8..d9235bcc 100644
--- a/compat/setenv.c
+++ b/compat/setenv.c
@@ -15,13 +15,15 @@
  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <sys/types.h>
+
 #include <stdlib.h>
 #include <string.h>
 
 #include "compat.h"
 
 int
-setenv(const char *name, const char *value, unused int overwrite)
+setenv(const char *name, const char *value, __unused int overwrite)
 {
 	char	*newval;
 
diff --git a/configure.ac b/configure.ac
index 31098d16..14a286b8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -454,7 +454,13 @@ else
 	AC_LIBOBJ(getopt)
 fi
 
-# Look for forkpty in libutil. compat/forkpty-*.c is linked if not found.
+# Look for fdforkpty and forkpty in libutil.
+AC_SEARCH_LIBS(fdforkpty, util, found_fdforkpty=yes, found_fdforkpty=no)
+if test "x$found_fdforkpty" = xyes; then
+	AC_DEFINE(HAVE_FDFORKPTY)
+else
+	AC_LIBOBJ(fdforkpty)
+fi
 AC_SEARCH_LIBS(forkpty, util, found_forkpty=yes, found_forkpty=no)
 if test "x$found_forkpty" = xyes; then
 	AC_DEFINE(HAVE_FORKPTY)