diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
index 63fb41df8..7f17de03d 100644
--- a/cmd/zdb/zdb.c
+++ b/cmd/zdb/zdb.c
@@ -1905,7 +1905,7 @@ dump_dedup_ratio(const ddt_stat_t *dds)
 }
 
 static void
-dump_ddt(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
+dump_ddt(ddt_t *ddt, ddt_type_t type, ddt_class_t class)
 {
 	char name[DDT_NAMELEN];
 	ddt_entry_t dde;
@@ -1965,8 +1965,8 @@ dump_all_ddts(spa_t *spa)
 
 	for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
 		ddt_t *ddt = spa->spa_ddt[c];
-		for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
-			for (enum ddt_class class = 0; class < DDT_CLASSES;
+		for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
+			for (ddt_class_t class = 0; class < DDT_CLASSES;
 			    class++) {
 				dump_ddt(ddt, type, class);
 			}
diff --git a/include/sys/ddt.h b/include/sys/ddt.h
index 25b8e7c9d..a11324209 100644
--- a/include/sys/ddt.h
+++ b/include/sys/ddt.h
@@ -41,22 +41,29 @@ struct abd;
 /*
  * On-disk DDT formats, in the desired search order (newest version first).
  */
-enum ddt_type {
+typedef enum {
 	DDT_TYPE_ZAP = 0,
 	DDT_TYPES
-};
+} ddt_type_t;
+
+_Static_assert(DDT_TYPES <= UINT8_MAX,
+	"ddt_type_t must fit in a uint8_t");
+
+/* New and updated entries recieve this type, see ddt_sync_entry() */
+#define	DDT_TYPE_DEFAULT	(DDT_TYPE_ZAP)
 
 /*
  * DDT classes, in the desired search order (highest replication level first).
  */
-enum ddt_class {
+typedef enum {
 	DDT_CLASS_DITTO = 0,
 	DDT_CLASS_DUPLICATE,
 	DDT_CLASS_UNIQUE,
 	DDT_CLASSES
-};
+} ddt_class_t;
 
-#define	DDT_TYPE_CURRENT		0
+_Static_assert(DDT_CLASSES < UINT8_MAX,
+	"ddt_class_t must fit in a uint8_t");
 
 /*
  * On-disk ddt entry:  key (name) and physical storage (value).
@@ -116,8 +123,8 @@ struct ddt_entry {
 	ddt_phys_t	dde_phys[DDT_PHYS_TYPES];
 	zio_t		*dde_lead_zio[DDT_PHYS_TYPES];
 	struct abd	*dde_repair_abd;
-	enum ddt_type	dde_type;
-	enum ddt_class	dde_class;
+	ddt_type_t	dde_type;
+	ddt_class_t	dde_class;
 	uint8_t		dde_loading;
 	uint8_t		dde_loaded;
 	kcondvar_t	dde_cv;
@@ -182,7 +189,7 @@ extern ddt_entry_t *ddt_lookup(ddt_t *ddt, const blkptr_t *bp, boolean_t add);
 extern void ddt_prefetch(spa_t *spa, const blkptr_t *bp);
 extern void ddt_remove(ddt_t *ddt, ddt_entry_t *dde);
 
-extern boolean_t ddt_class_contains(spa_t *spa, enum ddt_class max_class,
+extern boolean_t ddt_class_contains(spa_t *spa, ddt_class_t max_class,
     const blkptr_t *bp);
 
 extern ddt_entry_t *ddt_repair_start(ddt_t *ddt, const blkptr_t *bp);
diff --git a/include/sys/ddt_impl.h b/include/sys/ddt_impl.h
index c43ced5a7..9960f9666 100644
--- a/include/sys/ddt_impl.h
+++ b/include/sys/ddt_impl.h
@@ -70,14 +70,14 @@ extern void ddt_key_fill(ddt_key_t *ddk, const blkptr_t *bp);
 
 extern void ddt_stat_add(ddt_stat_t *dst, const ddt_stat_t *src, uint64_t neg);
 
-extern void ddt_object_name(ddt_t *ddt, enum ddt_type type,
-    enum ddt_class clazz, char *name);
-extern int ddt_object_walk(ddt_t *ddt, enum ddt_type type,
-    enum ddt_class clazz, uint64_t *walk, ddt_entry_t *dde);
-extern int ddt_object_count(ddt_t *ddt, enum ddt_type type,
-    enum ddt_class clazz, uint64_t *count);
-extern int ddt_object_info(ddt_t *ddt, enum ddt_type type,
-    enum ddt_class clazz, dmu_object_info_t *);
+extern void ddt_object_name(ddt_t *ddt, ddt_type_t type, ddt_class_t clazz,
+    char *name);
+extern int ddt_object_walk(ddt_t *ddt, ddt_type_t type, ddt_class_t clazz,
+    uint64_t *walk, ddt_entry_t *dde);
+extern int ddt_object_count(ddt_t *ddt, ddt_type_t type, ddt_class_t clazz,
+    uint64_t *count);
+extern int ddt_object_info(ddt_t *ddt, ddt_type_t type, ddt_class_t clazz,
+    dmu_object_info_t *);
 
 #ifdef	__cplusplus
 }
diff --git a/module/zfs/ddt.c b/module/zfs/ddt.c
index 321437c22..1b7063998 100644
--- a/module/zfs/ddt.c
+++ b/module/zfs/ddt.c
@@ -58,7 +58,7 @@ static const char *const ddt_class_name[DDT_CLASSES] = {
 };
 
 static void
-ddt_object_create(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_create(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     dmu_tx_t *tx)
 {
 	spa_t *spa = ddt->ddt_spa;
@@ -83,7 +83,7 @@ ddt_object_create(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 static void
-ddt_object_destroy(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_destroy(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     dmu_tx_t *tx)
 {
 	spa_t *spa = ddt->ddt_spa;
@@ -107,7 +107,7 @@ ddt_object_destroy(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 static int
-ddt_object_load(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
+ddt_object_load(ddt_t *ddt, ddt_type_t type, ddt_class_t class)
 {
 	ddt_object_t *ddo = &ddt->ddt_object_stats[type][class];
 	dmu_object_info_t doi;
@@ -147,7 +147,7 @@ ddt_object_load(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
 }
 
 static void
-ddt_object_sync(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_sync(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     dmu_tx_t *tx)
 {
 	ddt_object_t *ddo = &ddt->ddt_object_stats[type][class];
@@ -173,13 +173,13 @@ ddt_object_sync(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 static boolean_t
-ddt_object_exists(ddt_t *ddt, enum ddt_type type, enum ddt_class class)
+ddt_object_exists(ddt_t *ddt, ddt_type_t type, ddt_class_t class)
 {
 	return (!!ddt->ddt_object[type][class]);
 }
 
 static int
-ddt_object_lookup(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_lookup(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     ddt_entry_t *dde)
 {
 	if (!ddt_object_exists(ddt, type, class))
@@ -190,7 +190,7 @@ ddt_object_lookup(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 static void
-ddt_object_prefetch(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_prefetch(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     ddt_entry_t *dde)
 {
 	if (!ddt_object_exists(ddt, type, class))
@@ -201,7 +201,7 @@ ddt_object_prefetch(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 static int
-ddt_object_update(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_update(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     ddt_entry_t *dde, dmu_tx_t *tx)
 {
 	ASSERT(ddt_object_exists(ddt, type, class));
@@ -211,7 +211,7 @@ ddt_object_update(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 static int
-ddt_object_remove(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_remove(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     ddt_entry_t *dde, dmu_tx_t *tx)
 {
 	ASSERT(ddt_object_exists(ddt, type, class));
@@ -221,7 +221,7 @@ ddt_object_remove(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 int
-ddt_object_walk(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_walk(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     uint64_t *walk, ddt_entry_t *dde)
 {
 	ASSERT(ddt_object_exists(ddt, type, class));
@@ -231,7 +231,7 @@ ddt_object_walk(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 int
-ddt_object_count(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_count(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     uint64_t *count)
 {
 	ASSERT(ddt_object_exists(ddt, type, class));
@@ -241,7 +241,7 @@ ddt_object_count(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 int
-ddt_object_info(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_info(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     dmu_object_info_t *doi)
 {
 	if (!ddt_object_exists(ddt, type, class))
@@ -252,7 +252,7 @@ ddt_object_info(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
 }
 
 void
-ddt_object_name(ddt_t *ddt, enum ddt_type type, enum ddt_class class,
+ddt_object_name(ddt_t *ddt, ddt_type_t type, ddt_class_t class,
     char *name)
 {
 	(void) snprintf(name, DDT_NAMELEN, DMU_POOL_DDT,
@@ -460,8 +460,8 @@ ddt_lookup(ddt_t *ddt, const blkptr_t *bp, boolean_t add)
 {
 	ddt_key_t search;
 	ddt_entry_t *dde;
-	enum ddt_type type;
-	enum ddt_class class;
+	ddt_type_t type;
+	ddt_class_t class;
 	avl_index_t where;
 	int error;
 
@@ -536,8 +536,8 @@ ddt_prefetch(spa_t *spa, const blkptr_t *bp)
 	ddt = ddt_select(spa, bp);
 	ddt_key_fill(&dde.dde_key, bp);
 
-	for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
-		for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
+	for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
+		for (ddt_class_t class = 0; class < DDT_CLASSES; class++) {
 			ddt_object_prefetch(ddt, type, class, &dde);
 		}
 	}
@@ -625,8 +625,8 @@ ddt_load(spa_t *spa)
 
 	for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
 		ddt_t *ddt = spa->spa_ddt[c];
-		for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
-			for (enum ddt_class class = 0; class < DDT_CLASSES;
+		for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
+			for (ddt_class_t class = 0; class < DDT_CLASSES;
 			    class++) {
 				error = ddt_object_load(ddt, type, class);
 				if (error != 0 && error != ENOENT)
@@ -657,7 +657,7 @@ ddt_unload(spa_t *spa)
 }
 
 boolean_t
-ddt_class_contains(spa_t *spa, enum ddt_class max_class, const blkptr_t *bp)
+ddt_class_contains(spa_t *spa, ddt_class_t max_class, const blkptr_t *bp)
 {
 	ddt_t *ddt;
 	ddt_entry_t *dde;
@@ -673,8 +673,8 @@ ddt_class_contains(spa_t *spa, enum ddt_class max_class, const blkptr_t *bp)
 
 	ddt_key_fill(&(dde->dde_key), bp);
 
-	for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
-		for (enum ddt_class class = 0; class <= max_class; class++) {
+	for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
+		for (ddt_class_t class = 0; class <= max_class; class++) {
 			if (ddt_object_lookup(ddt, type, class, dde) == 0) {
 				kmem_cache_free(ddt_entry_cache, dde);
 				return (B_TRUE);
@@ -696,8 +696,8 @@ ddt_repair_start(ddt_t *ddt, const blkptr_t *bp)
 
 	dde = ddt_alloc(&ddk);
 
-	for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
-		for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
+	for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
+		for (ddt_class_t class = 0; class < DDT_CLASSES; class++) {
 			/*
 			 * We can only do repair if there are multiple copies
 			 * of the block.  For anything in the UNIQUE class,
@@ -796,10 +796,10 @@ ddt_sync_entry(ddt_t *ddt, ddt_entry_t *dde, dmu_tx_t *tx, uint64_t txg)
 	dsl_pool_t *dp = ddt->ddt_spa->spa_dsl_pool;
 	ddt_phys_t *ddp = dde->dde_phys;
 	ddt_key_t *ddk = &dde->dde_key;
-	enum ddt_type otype = dde->dde_type;
-	enum ddt_type ntype = DDT_TYPE_CURRENT;
-	enum ddt_class oclass = dde->dde_class;
-	enum ddt_class nclass;
+	ddt_type_t otype = dde->dde_type;
+	ddt_type_t ntype = DDT_TYPE_DEFAULT;
+	ddt_class_t oclass = dde->dde_class;
+	ddt_class_t nclass;
 	uint64_t total_refcnt = 0;
 
 	ASSERT(dde->dde_loaded);
@@ -883,9 +883,9 @@ ddt_sync_table(ddt_t *ddt, dmu_tx_t *tx, uint64_t txg)
 		ddt_free(dde);
 	}
 
-	for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
+	for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
 		uint64_t add, count = 0;
-		for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
+		for (ddt_class_t class = 0; class < DDT_CLASSES; class++) {
 			if (ddt_object_exists(ddt, type, class)) {
 				ddt_object_sync(ddt, type, class, tx);
 				VERIFY0(ddt_object_count(ddt, type, class,
@@ -893,7 +893,7 @@ ddt_sync_table(ddt_t *ddt, dmu_tx_t *tx, uint64_t txg)
 				count += add;
 			}
 		}
-		for (enum ddt_class class = 0; class < DDT_CLASSES; class++) {
+		for (ddt_class_t class = 0; class < DDT_CLASSES; class++) {
 			if (count == 0 && ddt_object_exists(ddt, type, class))
 				ddt_object_destroy(ddt, type, class, tx);
 		}
diff --git a/module/zfs/ddt_stats.c b/module/zfs/ddt_stats.c
index e1d367730..4ef6c3a07 100644
--- a/module/zfs/ddt_stats.c
+++ b/module/zfs/ddt_stats.c
@@ -132,8 +132,8 @@ ddt_get_dedup_object_stats(spa_t *spa, ddt_object_t *ddo_total)
 	/* Sum the statistics we cached in ddt_object_sync(). */
 	for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
 		ddt_t *ddt = spa->spa_ddt[c];
-		for (enum ddt_type type = 0; type < DDT_TYPES; type++) {
-			for (enum ddt_class class = 0; class < DDT_CLASSES;
+		for (ddt_type_t type = 0; type < DDT_TYPES; type++) {
+			for (ddt_class_t class = 0; class < DDT_CLASSES;
 			    class++) {
 				ddt_object_t *ddo =
 				    &ddt->ddt_object_stats[type][class];
@@ -156,8 +156,8 @@ ddt_get_dedup_histogram(spa_t *spa, ddt_histogram_t *ddh)
 {
 	for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
 		ddt_t *ddt = spa->spa_ddt[c];
-		for (enum ddt_type type = 0; type < DDT_TYPES && ddt; type++) {
-			for (enum ddt_class class = 0; class < DDT_CLASSES;
+		for (ddt_type_t type = 0; type < DDT_TYPES && ddt; type++) {
+			for (ddt_class_t class = 0; class < DDT_CLASSES;
 			    class++) {
 				ddt_histogram_add(ddh,
 				    &ddt->ddt_histogram_cache[type][class]);
diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index d04149f56..060a5cc36 100644
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -203,7 +203,7 @@ static uint_t zfs_scan_checkpoint_intval = 7200; /* in seconds */
 int zfs_scan_suspend_progress = 0; /* set to prevent scans from progressing */
 static int zfs_no_scrub_io = B_FALSE; /* set to disable scrub i/o */
 static int zfs_no_scrub_prefetch = B_FALSE; /* set to disable scrub prefetch */
-static const enum ddt_class zfs_scrub_ddt_class_max = DDT_CLASS_DUPLICATE;
+static const ddt_class_t zfs_scrub_ddt_class_max = DDT_CLASS_DUPLICATE;
 /* max number of blocks to free in a single TXG */
 static uint64_t zfs_async_block_max_blocks = UINT64_MAX;
 /* max number of dedup blocks to free in a single TXG */
@@ -2962,7 +2962,7 @@ dsl_scan_ddt_entry(dsl_scan_t *scn, enum zio_checksum checksum,
  * If there are N references to a deduped block, we don't want to scrub it
  * N times -- ideally, we should scrub it exactly once.
  *
- * We leverage the fact that the dde's replication class (enum ddt_class)
+ * We leverage the fact that the dde's replication class (ddt_class_t)
  * is ordered from highest replication class (DDT_CLASS_DITTO) to lowest
  * (DDT_CLASS_UNIQUE) so that we may walk the DDT in that order.
  *