diff --git a/include/os/freebsd/Makefile.am b/include/os/freebsd/Makefile.am
index d4103c2f06..292f79b8ce 100644
--- a/include/os/freebsd/Makefile.am
+++ b/include/os/freebsd/Makefile.am
@@ -20,7 +20,6 @@ noinst_HEADERS = \
 	%D%/spl/sys/debug.h \
 	%D%/spl/sys/dirent.h \
 	%D%/spl/sys/disp.h \
-	%D%/spl/sys/dkio.h \
 	%D%/spl/sys/fcntl.h \
 	%D%/spl/sys/file.h \
 	%D%/spl/sys/freebsd_rwlock.h \
diff --git a/include/os/freebsd/spl/sys/dkio.h b/include/os/freebsd/spl/sys/dkio.h
deleted file mode 100644
index cd747089d4..0000000000
--- a/include/os/freebsd/spl/sys/dkio.h
+++ /dev/null
@@ -1,34 +0,0 @@
-/*
- * CDDL HEADER START
- *
- * The contents of this file are subject to the terms of the
- * Common Development and Distribution License (the "License").
- * You may not use this file except in compliance with the License.
- *
- * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
- * or https://opensource.org/licenses/CDDL-1.0.
- * See the License for the specific language governing permissions
- * and limitations under the License.
- *
- * When distributing Covered Code, include this CDDL HEADER in each
- * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
- * If applicable, add the following below this CDDL HEADER, with the
- * fields enclosed by brackets "[]" replaced with your own identifying
- * information: Portions Copyright [yyyy] [name of copyright owner]
- *
- * CDDL HEADER END
- *
- * $FreeBSD$
- */
-/*
- * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
- * Use is subject to license terms.
- */
-
-#ifndef _OPENSOLARIS_SYS_DKIO_H_
-#define	_OPENSOLARIS_SYS_DKIO_H_
-
-#define	DKIOC		(0x04 << 8)
-#define	DKIOCFLUSHWRITECACHE	(DKIOC|34)	/* flush cache to phys medium */
-
-#endif /* _OPENSOLARIS_SYS_DKIO_H_ */
diff --git a/include/os/linux/Makefile.am b/include/os/linux/Makefile.am
index 332569efe3..f31ae50b96 100644
--- a/include/os/linux/Makefile.am
+++ b/include/os/linux/Makefile.am
@@ -63,7 +63,6 @@ kernel_spl_sys_HEADERS = \
 	%D%/spl/sys/ctype.h \
 	%D%/spl/sys/debug.h \
 	%D%/spl/sys/disp.h \
-	%D%/spl/sys/dkio.h \
 	%D%/spl/sys/errno.h \
 	%D%/spl/sys/fcntl.h \
 	%D%/spl/sys/file.h \
diff --git a/include/os/linux/spl/sys/dkio.h b/include/os/linux/spl/sys/dkio.h
deleted file mode 100644
index a90b67d367..0000000000
--- a/include/os/linux/spl/sys/dkio.h
+++ /dev/null
@@ -1,39 +0,0 @@
-/*
- *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
- *  Copyright (C) 2007 The Regents of the University of California.
- *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
- *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
- *  UCRL-CODE-235197
- *
- *  This file is part of the SPL, Solaris Porting Layer.
- *
- *  The SPL is free software; you can redistribute it and/or modify it
- *  under the terms of the GNU General Public License as published by the
- *  Free Software Foundation; either version 2 of the License, or (at your
- *  option) any later version.
- *
- *  The SPL is distributed in the hope that it will be useful, but WITHOUT
- *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- *  for more details.
- *
- *  You should have received a copy of the GNU General Public License along
- *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef _SPL_DKIO_H
-#define	_SPL_DKIO_H
-
-#define	DFL_SZ(num_exts) \
-	(sizeof (dkioc_free_list_t) + (num_exts - 1) * 16)
-
-#define	DKIOC		(0x04 << 8)
-#define	DKIOCFLUSHWRITECACHE	(DKIOC|34)	/* flush cache to phys medium */
-
-/*
- * ioctl to free space (e.g. SCSI UNMAP) off a disk.
- * Pass a dkioc_free_list_t containing a list of extents to be freed.
- */
-#define	DKIOCFREE	(DKIOC|50)
-
-#endif /* _SPL_DKIO_H */
diff --git a/include/sys/vdev_impl.h b/include/sys/vdev_impl.h
index 2a93f7c680..95164c4546 100644
--- a/include/sys/vdev_impl.h
+++ b/include/sys/vdev_impl.h
@@ -35,7 +35,6 @@
 #include <sys/nvpair.h>
 #include <sys/space_map.h>
 #include <sys/vdev.h>
-#include <sys/dkio.h>
 #include <sys/uberblock_impl.h>
 #include <sys/vdev_indirect_mapping.h>
 #include <sys/vdev_indirect_births.h>