diff --git a/include/sys/vdev_impl.h b/include/sys/vdev_impl.h
index 2b22b973ba..5f4e82ad86 100644
--- a/include/sys/vdev_impl.h
+++ b/include/sys/vdev_impl.h
@@ -420,6 +420,7 @@ struct vdev {
 	boolean_t	vdev_copy_uberblocks;  /* post expand copy uberblocks */
 	boolean_t	vdev_resilver_deferred;  /* resilver deferred */
 	boolean_t	vdev_kobj_flag; /* kobj event record */
+	boolean_t	vdev_attaching; /* vdev attach ashift handling */
 	vdev_queue_t	vdev_queue;	/* I/O deadline schedule queue	*/
 	spa_aux_vdev_t	*vdev_aux;	/* for l2cache and spares vdevs	*/
 	zio_t		*vdev_probe_zio; /* root of current probe	*/
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 30551feb63..1199bf5d32 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -889,9 +889,15 @@ vdev_alloc(spa_t *spa, vdev_t **vdp, nvlist_t *nv, vdev_t *parent, uint_t id,
 	    &vd->vdev_not_present);
 
 	/*
-	 * Get the alignment requirement.
+	 * Get the alignment requirement. Ignore pool ashift for vdev
+	 * attach case.
 	 */
-	(void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_ASHIFT, &vd->vdev_ashift);
+	if (alloctype != VDEV_ALLOC_ATTACH) {
+		(void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_ASHIFT,
+		    &vd->vdev_ashift);
+	} else {
+		vd->vdev_attaching = B_TRUE;
+	}
 
 	/*
 	 * Retrieve the vdev creation time.
@@ -2144,9 +2150,9 @@ vdev_open(vdev_t *vd)
 				return (SET_ERROR(EDOM));
 			}
 
-			if (vd->vdev_top == vd) {
+			if (vd->vdev_top == vd && vd->vdev_attaching == B_FALSE)
 				vdev_ashift_optimize(vd);
-			}
+			vd->vdev_attaching = B_FALSE;
 		}
 		if (vd->vdev_ashift != 0 && (vd->vdev_ashift < ASHIFT_MIN ||
 		    vd->vdev_ashift > ASHIFT_MAX)) {
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_attach/attach-o_ashift.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_attach/attach-o_ashift.ksh
index 6ccec6abd6..574cb7654d 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_attach/attach-o_ashift.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_attach/attach-o_ashift.ksh
@@ -35,7 +35,7 @@
 #
 # STRATEGY:
 #	1. Create various pools with different ashift values.
-#	2. Verify 'attach -o ashift=<n>' works only with allowed values.
+#	2. Verify 'attach' works.
 #
 
 verify_runnable "global"
@@ -66,26 +66,14 @@ log_must set_tunable32 VDEV_FILE_PHYSICAL_ASHIFT 16
 typeset ashifts=("9" "10" "11" "12" "13" "14" "15" "16")
 for ashift in ${ashifts[@]}
 do
-	for cmdval in ${ashifts[@]}
-	do
-		log_must zpool create -o ashift=$ashift $TESTPOOL1 $disk1
-		log_must verify_ashift $disk1 $ashift
-
-		# ashift_of(attached_disk) <= ashift_of(existing_vdev)
-		if [[ $cmdval -le $ashift ]]
-		then
-			log_must zpool attach -o ashift=$cmdval $TESTPOOL1 \
-			    $disk1 $disk2
-			log_must verify_ashift $disk2 $ashift
-		else
-			log_mustnot zpool attach -o ashift=$cmdval $TESTPOOL1 \
-			    $disk1 $disk2
-		fi
-		# clean things for the next run
-		log_must zpool destroy $TESTPOOL1
-		log_must zpool labelclear $disk1
-		log_must zpool labelclear $disk2
-	done
+	log_must zpool create -o ashift=$ashift $TESTPOOL1 $disk1
+	log_must verify_ashift $disk1 $ashift
+	log_must zpool attach $TESTPOOL1 $disk1 $disk2
+	log_must verify_ashift $disk2 $ashift
+	# clean things for the next run
+	log_must zpool destroy $TESTPOOL1
+	log_must zpool labelclear $disk1
+	log_must zpool labelclear $disk2
 done
 
 typeset badvals=("off" "on" "1" "8" "17" "1b" "ff" "-")
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace-o_ashift.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace-o_ashift.ksh
index 37ed0062e6..9595e51241 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace-o_ashift.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace-o_ashift.ksh
@@ -35,7 +35,7 @@
 #
 # STRATEGY:
 #	1. Create various pools with different ashift values.
-#	2. Verify 'replace -o ashift=<n>' works only with allowed values.
+#	2. Verify 'replace' works.
 #
 
 verify_runnable "global"
@@ -66,26 +66,16 @@ log_must set_tunable32 VDEV_FILE_PHYSICAL_ASHIFT 16
 typeset ashifts=("9" "10" "11" "12" "13" "14" "15" "16")
 for ashift in ${ashifts[@]}
 do
-	for cmdval in ${ashifts[@]}
-	do
-		log_must zpool create -o ashift=$ashift $TESTPOOL1 $disk1
-		log_must verify_ashift $disk1 $ashift
-		# ashift_of(replacing_disk) <= ashift_of(existing_vdev)
-		if [[ $cmdval -le $ashift ]]
-		then
-			log_must zpool replace -o ashift=$cmdval $TESTPOOL1 \
-			    $disk1 $disk2
-			log_must verify_ashift $disk2 $ashift
-			wait_replacing $TESTPOOL1
-		else
-			log_mustnot zpool replace -o ashift=$cmdval $TESTPOOL1 \
-			    $disk1 $disk2
-		fi
-		# clean things for the next run
-		log_must zpool destroy $TESTPOOL1
-		log_must zpool labelclear $disk1
-		log_must zpool labelclear $disk2
-	done
+	log_must zpool create -o ashift=$ashift $TESTPOOL1 $disk1
+	log_must verify_ashift $disk1 $ashift
+	# ashift_of(replacing_disk) <= ashift_of(existing_vdev)
+	log_must zpool replace $TESTPOOL1 $disk1 $disk2
+	log_must verify_ashift $disk2 $ashift
+	wait_replacing $TESTPOOL1
+	# clean things for the next run
+	log_must zpool destroy $TESTPOOL1
+	log_must zpool labelclear $disk1
+	log_must zpool labelclear $disk2
 done
 
 typeset badvals=("off" "on" "1" "8" "17" "1b" "ff" "-")
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace_prop_ashift.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace_prop_ashift.ksh
index ffdaf91a28..b4ac18e5ea 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace_prop_ashift.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_replace/replace_prop_ashift.ksh
@@ -34,10 +34,8 @@
 #
 # STRATEGY:
 #	1. Create a pool with default values.
-#	2. Verify 'zpool replace' uses the ashift pool property value when
-#	   replacing an existing device.
-#	3. Verify the default ashift value can still be overridden by manually
-#	   specifying '-o ashift=<n>' from the command line.
+#	2. Override the pool ashift property.
+#	3. Verify 'zpool replace' works.
 #
 
 verify_runnable "global"
@@ -72,21 +70,9 @@ do
 	do
 		log_must zpool create -o ashift=$ashift $TESTPOOL1 $disk1
 		log_must zpool set ashift=$pprop $TESTPOOL1
-		# ashift_of(replacing_disk) <= ashift_of(existing_vdev)
-		if [[ $pprop -le $ashift ]]
-		then
-			log_must zpool replace $TESTPOOL1 $disk1 $disk2
-			wait_replacing $TESTPOOL1
-			log_must verify_ashift $disk2 $ashift
-		else
-			# cannot replace if pool prop ashift > vdev ashift
-			log_mustnot zpool replace $TESTPOOL1 $disk1 $disk2
-			# verify we can override the pool prop value manually
-			log_must zpool replace -o ashift=$ashift $TESTPOOL1 \
-			    $disk1 $disk2
-			wait_replacing $TESTPOOL1
-			log_must verify_ashift $disk2 $ashift
-		fi
+		log_must zpool replace $TESTPOOL1 $disk1 $disk2
+		wait_replacing $TESTPOOL1
+		log_must verify_ashift $disk2 $ashift
 		# clean things for the next run
 		log_must zpool destroy $TESTPOOL1
 		log_must zpool labelclear $disk1