diff --git a/sys/dev/mem/memutil.c b/sys/dev/mem/memutil.c
--- a/sys/dev/mem/memutil.c
+++ b/sys/dev/mem/memutil.c
@@ -26,15 +26,14 @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <sys/param.h>
+#include <sys/systm.h>
 #include <sys/kernel.h>
 #include <sys/lock.h>
 #include <sys/malloc.h>
 #include <sys/memrange.h>
-#include <sys/rwlock.h>
-#include <sys/systm.h>
+#include <sys/sx.h>
 
-static struct rwlock	mr_lock;
+static struct sx	mr_lock;
 
 /*
  * Implementation-neutral, kernel-callable functions for manipulating
@@ -46,7 +45,7 @@
 
 	if (mem_range_softc.mr_op == NULL)
 		return;
-	rw_init(&mr_lock, "memrange");
+	sx_init(&mr_lock, "memrange");
 	mem_range_softc.mr_op->init(&mem_range_softc);
 }
 
@@ -56,7 +55,7 @@
 
 	if (mem_range_softc.mr_op == NULL)
 		return;
-	rw_destroy(&mr_lock);
+	sx_destroy(&mr_lock);
 }
 
 int
@@ -67,12 +66,12 @@
 	if (mem_range_softc.mr_op == NULL)
 		return (EOPNOTSUPP);
 	nd = *arg;
-	rw_rlock(&mr_lock);
+	sx_slock(&mr_lock);
 	if (nd == 0)
 		*arg = mem_range_softc.mr_ndesc;
 	else
 		bcopy(mem_range_softc.mr_desc, mrd, nd * sizeof(*mrd));
-	rw_runlock(&mr_lock);
+	sx_sunlock(&mr_lock);
 	return (0);
 }
 
@@ -83,8 +82,8 @@
 
 	if (mem_range_softc.mr_op == NULL)
 		return (EOPNOTSUPP);
-	rw_wlock(&mr_lock);
+	sx_xlock(&mr_lock);
 	ret = mem_range_softc.mr_op->set(&mem_range_softc, mrd, arg);
-	rw_wunlock(&mr_lock);
+	sx_xunlock(&mr_lock);
 	return (ret);
 }