diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 62c4be832b..f395414c9d 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -2176,7 +2176,7 @@ get_interval_count(int *argcp, char **argv, unsigned long *iv,
     unsigned long *cnt)
 {
 	unsigned long interval = 0, count = 0;
-	int argc = *argcp, errno;
+	int argc = *argcp;
 
 	/*
 	 * Determine if the last argument is an integer or a pool name
diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index 273bae9c63..f254337e96 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -2303,7 +2303,7 @@ dbuf_write_ready(zio_t *zio, arc_buf_t *buf, void *vdb)
 
 #ifdef ZFS_DEBUG
 	if (db->db_blkid == DMU_SPILL_BLKID) {
-		dnode_t *dn = db->db_dnode;
+		ASSERTV(dnode_t *dn = db->db_dnode);
 		ASSERT(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR);
 		ASSERT(!(BP_IS_HOLE(db->db_blkptr)) &&
 		    db->db_blkptr == &dn->dn_phys->dn_spill);
@@ -2382,7 +2382,7 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 
 #ifdef ZFS_DEBUG
 	if (db->db_blkid == DMU_SPILL_BLKID) {
-		dnode_t *dn = db->db_dnode;
+		ASSERTV(dnode_t *dn = db->db_dnode);
 		ASSERT(dn->dn_phys->dn_flags & DNODE_FLAG_SPILL_BLKPTR);
 		ASSERT(!(BP_IS_HOLE(db->db_blkptr)) &&
 		    db->db_blkptr == &dn->dn_phys->dn_spill);
diff --git a/module/zfs/dmu.c b/module/zfs/dmu.c
index 5b87c81c63..aafcc8cf4e 100644
--- a/module/zfs/dmu.c
+++ b/module/zfs/dmu.c
@@ -1146,8 +1146,8 @@ dmu_sync_ready(zio_t *zio, arc_buf_t *buf, void *varg)
 {
 	dmu_sync_arg_t *dsa = varg;
 	dmu_buf_t *db = dsa->dsa_zgd->zgd_db;
-	dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode;
 	blkptr_t *bp = zio->io_bp;
+	ASSERTV(dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode);
 
 	if (zio->io_error == 0) {
 		if (BP_IS_HOLE(bp)) {
diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c
index 3aea0f321e..690e6ecdee 100644
--- a/module/zfs/dmu_objset.c
+++ b/module/zfs/dmu_objset.c
@@ -954,7 +954,6 @@ dmu_objset_write_ready(zio_t *zio, arc_buf_t *abuf, void *arg)
 	blkptr_t *bp = zio->io_bp;
 	objset_t *os = arg;
 	dnode_phys_t *dnp = &os->os_phys->os_meta_dnode;
-	ASSERTV(blkptr_t *bp_orig = &zio->io_bp_orig);
 
 	ASSERT(bp == os->os_rootbp);
 	ASSERT(BP_GET_TYPE(bp) == DMU_OT_OBJSET);
diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index 53413ef194..a6361da12d 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -1466,8 +1466,8 @@ static void
 remove_from_next_clones(dsl_dataset_t *ds, uint64_t obj, dmu_tx_t *tx)
 {
 	objset_t *mos = ds->ds_dir->dd_pool->dp_meta_objset;
-	uint64_t count;
 	int err;
+	ASSERTV(uint64_t count);
 
 	ASSERT(ds->ds_phys->ds_num_children >= 2);
 	err = zap_remove_int(mos, ds->ds_phys->ds_next_clones_obj, obj, tx);
@@ -2474,7 +2474,6 @@ struct promotearg {
 };
 
 static int snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep);
-static boolean_t snaplist_unstable(list_t *l);
 
 static int
 dsl_dataset_promote_check(void *arg1, void *arg2, dmu_tx_t *tx)
diff --git a/module/zfs/sa.c b/module/zfs/sa.c
index a91b379f99..a61030661e 100644
--- a/module/zfs/sa.c
+++ b/module/zfs/sa.c
@@ -1121,9 +1121,9 @@ sa_byteswap(sa_handle_t *hdl, sa_buf_type_t buftype)
 {
 	sa_hdr_phys_t *sa_hdr_phys = SA_GET_HDR(hdl, buftype);
 	dmu_buf_impl_t *db;
-	sa_os_t *sa = hdl->sa_os->os_sa;
 	int num_lengths = 1;
 	int i;
+	ASSERTV(sa_os_t *sa = hdl->sa_os->os_sa);
 
 	ASSERT(MUTEX_HELD(&sa->sa_lock));
 	if (sa_hdr_phys->sa_magic == SA_MAGIC)
@@ -1224,7 +1224,7 @@ sa_idx_tab_rele(objset_t *os, void *arg)
 static void
 sa_idx_tab_hold(objset_t *os, sa_idx_tab_t *idx_tab)
 {
-	sa_os_t *sa = os->os_sa;
+	ASSERTV(sa_os_t *sa = os->os_sa);
 
 	ASSERT(MUTEX_HELD(&sa->sa_lock));
 	(void) refcount_add(&idx_tab->sa_refcount, NULL);
@@ -1260,10 +1260,10 @@ sa_handle_get_from_db(objset_t *os, dmu_buf_t *db, void *userp,
     sa_handle_type_t hdl_type, sa_handle_t **handlepp)
 {
 	int error = 0;
-	dmu_object_info_t doi;
 	sa_handle_t *handle;
-
 #ifdef ZFS_DEBUG
+	dmu_object_info_t doi;
+
 	dmu_object_info_from_db(db, &doi);
 	ASSERT(doi.doi_bonus_type == DMU_OT_SA ||
 	    doi.doi_bonus_type == DMU_OT_ZNODE);
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index ad88f83719..1ec6e8ad6e 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -1401,8 +1401,8 @@ vdev_validate(vdev_t *vd)
 void
 vdev_close(vdev_t *vd)
 {
-	ASSERTV(spa_t *spa = vd->vdev_spa);
 	vdev_t *pvd = vd->vdev_parent;
+	ASSERTV(spa_t *spa = vd->vdev_spa);
 
 	ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);
 
diff --git a/module/zfs/zap_micro.c b/module/zfs/zap_micro.c
index 52a7e4f57c..d01f2e5c8e 100644
--- a/module/zfs/zap_micro.c
+++ b/module/zfs/zap_micro.c
@@ -1043,12 +1043,13 @@ zap_update(objset_t *os, uint64_t zapobj, const char *name,
 {
 	zap_t *zap;
 	mzap_ent_t *mze;
-	uint64_t oldval;
 	const uint64_t *intval = val;
 	zap_name_t *zn;
 	int err;
 
 #ifdef ZFS_DEBUG
+	uint64_t oldval;
+
 	/*
 	 * If there is an old value, it shouldn't change across the
 	 * lockdir (eg, due to bprewrite's xlation).
diff --git a/module/zfs/zil.c b/module/zfs/zil.c
index 4aa4d10b07..f2f75b087e 100644
--- a/module/zfs/zil.c
+++ b/module/zfs/zil.c
@@ -78,8 +78,6 @@ boolean_t zfs_nocacheflush = B_FALSE;
 
 static kmem_cache_t *zil_lwb_cache;
 
-static boolean_t zil_empty(zilog_t *zilog);
-
 #define	LWB_EMPTY(lwb) ((BP_GET_LSIZE(&lwb->lwb_blk) - \
     sizeof (zil_chain_t)) == (lwb->lwb_sz - lwb->lwb_nused))
 
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index f7bb42b943..663f9f94cb 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1939,12 +1939,12 @@ static void
 zio_ddt_ditto_write_done(zio_t *zio)
 {
 	int p = DDT_PHYS_DITTO;
-	zio_prop_t *zp = &zio->io_prop;
 	blkptr_t *bp = zio->io_bp;
 	ddt_t *ddt = ddt_select(zio->io_spa, bp);
 	ddt_entry_t *dde = zio->io_private;
 	ddt_phys_t *ddp = &dde->dde_phys[p];
 	ddt_key_t *ddk = &dde->dde_key;
+	ASSERTV(zio_prop_t *zp = &zio->io_prop);
 
 	ddt_enter(ddt);