diff --git a/module/zfs/ddt.c b/module/zfs/ddt.c
index 7420173cc9..abf371ce6d 100644
--- a/module/zfs/ddt.c
+++ b/module/zfs/ddt.c
@@ -499,6 +499,7 @@ ddt_get_dedup_stats(spa_t *spa, ddt_stat_t *dds_total)
 {
 	ddt_histogram_t *ddh_total;
 
+	/* XXX: Move to a slab */
 	ddh_total = kmem_zalloc(sizeof (ddt_histogram_t), KM_SLEEP);
 	ddt_get_dedup_histogram(spa, ddh_total);
 	ddt_histogram_stat(dds_total, ddh_total);
@@ -647,6 +648,7 @@ ddt_alloc(const ddt_key_t *ddk)
 {
 	ddt_entry_t *dde;
 
+	/* XXX: Move to a slab */
 	dde = kmem_zalloc(sizeof (ddt_entry_t), KM_SLEEP);
 	cv_init(&dde->dde_cv, NULL, CV_DEFAULT, NULL);
 
@@ -795,7 +797,8 @@ ddt_table_alloc(spa_t *spa, enum zio_checksum c)
 {
 	ddt_t *ddt;
 
-	ddt = kmem_zalloc(sizeof (*ddt), KM_SLEEP);
+	/* XXX: Move to a slab */
+	ddt = kmem_zalloc(sizeof (*ddt), KM_SLEEP | KM_NODEBUG);
 
 	mutex_init(&ddt->ddt_lock, NULL, MUTEX_DEFAULT, NULL);
 	avl_create(&ddt->ddt_tree, ddt_entry_compare,
diff --git a/module/zfs/spa_history.c b/module/zfs/spa_history.c
index 7eb928519f..d5ce9ad105 100644
--- a/module/zfs/spa_history.c
+++ b/module/zfs/spa_history.c
@@ -441,11 +441,7 @@ log_internal(history_internal_events_t event, spa_t *spa,
 		return;
 
 	ha = kmem_alloc(sizeof (history_arg_t), KM_SLEEP);
-	ha->ha_history_str = kmem_alloc(vsnprintf(NULL, 0, fmt, adx) + 1,
-	    KM_SLEEP);
-
-	(void) vsprintf(ha->ha_history_str, fmt, adx);
-
+	ha->ha_history_str = kmem_asprintf(fmt, adx);
 	ha->ha_log_type = LOG_INTERNAL;
 	ha->ha_event = event;
 	ha->ha_zone = NULL;