diff --git a/include/sys/zio.h b/include/sys/zio.h
index 9ae755168991..d3b95e17093f 100644
--- a/include/sys/zio.h
+++ b/include/sys/zio.h
@@ -477,7 +477,7 @@ extern zio_t *zio_write_phys(zio_t *pio, vdev_t *vd, uint64_t offset,
     boolean_t labels);
 
 extern zio_t *zio_free_sync(zio_t *pio, spa_t *spa, uint64_t txg,
-    const blkptr_t *bp, enum zio_flag flags);
+    const blkptr_t *bp, uint64_t size, enum zio_flag flags);
 
 extern int zio_alloc_zil(spa_t *spa, uint64_t txg, blkptr_t *new_bp,
     blkptr_t *old_bp, uint64_t size, boolean_t use_slog);
diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index 07e3dec1ecec..91b467e6ccee 100644
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -360,7 +360,8 @@ void
 dsl_free_sync(zio_t *pio, dsl_pool_t *dp, uint64_t txg, const blkptr_t *bpp)
 {
 	ASSERT(dsl_pool_sync_context(dp));
-	zio_nowait(zio_free_sync(pio, dp->dp_spa, txg, bpp, pio->io_flags));
+	zio_nowait(zio_free_sync(pio, dp->dp_spa, txg, bpp, BP_GET_PSIZE(bpp),
+	    pio->io_flags));
 }
 
 int
@@ -1431,7 +1432,7 @@ dsl_scan_free_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 		return (ERESTART);
 
 	zio_nowait(zio_free_sync(scn->scn_zio_root, scn->scn_dp->dp_spa,
-	    dmu_tx_get_txg(tx), bp, 0));
+	    dmu_tx_get_txg(tx), bp, BP_GET_PSIZE(bp), 0));
 	dsl_dir_diduse_space(tx->tx_pool->dp_free_dir, DD_USED_HEAD,
 	    -bp_get_dsize_sync(scn->scn_dp->dp_spa, bp),
 	    -BP_GET_PSIZE(bp), -BP_GET_UCSIZE(bp), tx);
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 04b3cfb361e5..16df287acb7f 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -5288,7 +5288,7 @@ spa_free_sync_cb(void *arg, const blkptr_t *bp, dmu_tx_t *tx)
 	zio_t *zio = arg;
 
 	zio_nowait(zio_free_sync(zio, zio->io_spa, dmu_tx_get_txg(tx), bp,
-	    zio->io_flags));
+	    BP_GET_PSIZE(bp), zio->io_flags));
 	return (0);
 }
 
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index 0cc98687daf4..76d48aa4f9c5 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -757,7 +757,7 @@ zio_free(spa_t *spa, uint64_t txg, const blkptr_t *bp)
 
 zio_t *
 zio_free_sync(zio_t *pio, spa_t *spa, uint64_t txg, const blkptr_t *bp,
-    enum zio_flag flags)
+    uint64_t size, enum zio_flag flags)
 {
 	zio_t *zio;
 
@@ -768,7 +768,7 @@ zio_free_sync(zio_t *pio, spa_t *spa, uint64_t txg, const blkptr_t *bp,
 	ASSERT(spa_syncing_txg(spa) == txg);
 	ASSERT(spa_sync_pass(spa) <= SYNC_PASS_DEFERRED_FREE);
 
-	zio = zio_create(pio, spa, txg, bp, NULL, BP_GET_PSIZE(bp),
+	zio = zio_create(pio, spa, txg, bp, NULL, size,
 	    NULL, NULL, ZIO_TYPE_FREE, ZIO_PRIORITY_FREE, flags,
 	    NULL, 0, NULL, ZIO_STAGE_OPEN, ZIO_FREE_PIPELINE);
 
@@ -1594,7 +1594,7 @@ zio_t *
 zio_free_gang(zio_t *pio, blkptr_t *bp, zio_gang_node_t *gn, void *data)
 {
 	return (zio_free_sync(pio, pio->io_spa, pio->io_txg, bp,
-	    ZIO_GANG_CHILD_FLAGS(pio)));
+	    SPA_GANGBLOCKSIZE, ZIO_GANG_CHILD_FLAGS(pio)));
 }
 
 /* ARGSUSED */
@@ -1730,7 +1730,7 @@ zio_gang_tree_issue(zio_t *pio, zio_gang_node_t *gn, blkptr_t *bp, void *data)
 		}
 	}
 
-	if (gn == gio->io_gang_tree)
+	if (gn == gio->io_gang_tree && gio->io_data != NULL)
 		ASSERT3P((char *)gio->io_data + gio->io_size, ==, data);
 
 	if (zio != pio)