diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
index 012d009dc..11af8c0c3 100644
--- a/cmd/zdb/zdb.c
+++ b/cmd/zdb/zdb.c
@@ -87,7 +87,7 @@ libzfs_handle_t *g_zfs;
  * debugging facilities.
  */
 const char *
-_umem_debug_init()
+_umem_debug_init(void)
 {
 	return ("default,verbose"); /* $UMEM_DEBUG setting */
 }
@@ -1221,7 +1221,7 @@ static boolean_t sa_loaded;
 sa_attr_type_t *sa_attr_table;
 
 static void
-fuid_table_destroy()
+fuid_table_destroy(void)
 {
 	if (fuid_table_loaded) {
 		zfs_fuid_table_destroy(&idx_tree, &domain_tree);
diff --git a/cmd/zdb/zdb_il.c b/cmd/zdb/zdb_il.c
index a0ed985f5..257aa6f4b 100644
--- a/cmd/zdb/zdb_il.c
+++ b/cmd/zdb/zdb_il.c
@@ -240,7 +240,7 @@ zil_prt_rec_acl(zilog_t *zilog, int txtype, lr_acl_t *lr)
 	    (u_longlong_t)lr->lr_foid, (u_longlong_t)lr->lr_aclcnt);
 }
 
-typedef void (*zil_prt_rec_func_t)();
+typedef void (*zil_prt_rec_func_t)(zilog_t *, int, void *);
 typedef struct zil_rec_info {
 	zil_prt_rec_func_t	zri_print;
 	char			*zri_name;
@@ -248,27 +248,27 @@ typedef struct zil_rec_info {
 } zil_rec_info_t;
 
 static zil_rec_info_t zil_rec_info[TX_MAX_TYPE] = {
-	{	NULL,			"Total              " },
-	{	zil_prt_rec_create,	"TX_CREATE          " },
-	{	zil_prt_rec_create,	"TX_MKDIR           " },
-	{	zil_prt_rec_create,	"TX_MKXATTR         " },
-	{	zil_prt_rec_create,	"TX_SYMLINK         " },
-	{	zil_prt_rec_remove,	"TX_REMOVE          " },
-	{	zil_prt_rec_remove,	"TX_RMDIR           " },
-	{	zil_prt_rec_link,	"TX_LINK            " },
-	{	zil_prt_rec_rename,	"TX_RENAME          " },
-	{	zil_prt_rec_write,	"TX_WRITE           " },
-	{	zil_prt_rec_truncate,	"TX_TRUNCATE        " },
-	{	zil_prt_rec_setattr,	"TX_SETATTR         " },
-	{	zil_prt_rec_acl,	"TX_ACL_V0          " },
-	{	zil_prt_rec_acl,	"TX_ACL_ACL         " },
-	{	zil_prt_rec_create,	"TX_CREATE_ACL      " },
-	{	zil_prt_rec_create,	"TX_CREATE_ATTR     " },
-	{	zil_prt_rec_create,	"TX_CREATE_ACL_ATTR " },
-	{	zil_prt_rec_create,	"TX_MKDIR_ACL       " },
-	{	zil_prt_rec_create,	"TX_MKDIR_ATTR      " },
-	{	zil_prt_rec_create,	"TX_MKDIR_ACL_ATTR  " },
-	{	zil_prt_rec_write,	"TX_WRITE2          " },
+	{ NULL,			"Total              " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_CREATE          " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_MKDIR           " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_MKXATTR         " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_SYMLINK         " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_remove,	"TX_REMOVE          " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_remove,	"TX_RMDIR           " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_link,		"TX_LINK            " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_rename,	"TX_RENAME          " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_write,	"TX_WRITE           " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_truncate,	"TX_TRUNCATE        " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_setattr,	"TX_SETATTR         " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_acl,		"TX_ACL_V0          " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_acl,		"TX_ACL_ACL         " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_CREATE_ACL      " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_CREATE_ATTR     " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_CREATE_ACL_ATTR " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_MKDIR_ACL       " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_MKDIR_ATTR      " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_create,	"TX_MKDIR_ACL_ATTR  " },
+	{ (zil_prt_rec_func_t)zil_prt_rec_write,	"TX_WRITE2          " },
 };
 
 /* ARGSUSED */
diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index 5e21e620d..fbc3c2cc9 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -359,7 +359,7 @@ static void usage(boolean_t) __NORETURN;
  * debugging facilities.
  */
 const char *
-_umem_debug_init()
+_umem_debug_init(void)
 {
 	return ("default,verbose"); /* $UMEM_DEBUG setting */
 }
@@ -1579,26 +1579,26 @@ ztest_replay_setattr(ztest_ds_t *zd, lr_setattr_t *lr, boolean_t byteswap)
 }
 
 zil_replay_func_t *ztest_replay_vector[TX_MAX_TYPE] = {
-	NULL,			/* 0 no such transaction type */
-	ztest_replay_create,	/* TX_CREATE */
-	NULL,			/* TX_MKDIR */
-	NULL,			/* TX_MKXATTR */
-	NULL,			/* TX_SYMLINK */
-	ztest_replay_remove,	/* TX_REMOVE */
-	NULL,			/* TX_RMDIR */
-	NULL,			/* TX_LINK */
-	NULL,			/* TX_RENAME */
-	ztest_replay_write,	/* TX_WRITE */
-	ztest_replay_truncate,	/* TX_TRUNCATE */
-	ztest_replay_setattr,	/* TX_SETATTR */
-	NULL,			/* TX_ACL */
-	NULL,			/* TX_CREATE_ACL */
-	NULL,			/* TX_CREATE_ATTR */
-	NULL,			/* TX_CREATE_ACL_ATTR */
-	NULL,			/* TX_MKDIR_ACL */
-	NULL,			/* TX_MKDIR_ATTR */
-	NULL,			/* TX_MKDIR_ACL_ATTR */
-	NULL,			/* TX_WRITE2 */
+	NULL,				/* 0 no such transaction type */
+	(zil_replay_func_t *)ztest_replay_create,	/* TX_CREATE */
+	NULL,						/* TX_MKDIR */
+	NULL,						/* TX_MKXATTR */
+	NULL,						/* TX_SYMLINK */
+	(zil_replay_func_t *)ztest_replay_remove,	/* TX_REMOVE */
+	NULL,						/* TX_RMDIR */
+	NULL,						/* TX_LINK */
+	NULL,						/* TX_RENAME */
+	(zil_replay_func_t *)ztest_replay_write,	/* TX_WRITE */
+	(zil_replay_func_t *)ztest_replay_truncate,	/* TX_TRUNCATE */
+	(zil_replay_func_t *)ztest_replay_setattr,	/* TX_SETATTR */
+	NULL,						/* TX_ACL */
+	NULL,						/* TX_CREATE_ACL */
+	NULL,						/* TX_CREATE_ATTR */
+	NULL,						/* TX_CREATE_ACL_ATTR */
+	NULL,						/* TX_MKDIR_ACL */
+	NULL,						/* TX_MKDIR_ATTR */
+	NULL,						/* TX_MKDIR_ACL_ATTR */
+	NULL,						/* TX_WRITE2 */
 };
 
 /*
@@ -5379,7 +5379,7 @@ print_time(hrtime_t t, char *timebuf)
 }
 
 static nvlist_t *
-make_random_props()
+make_random_props(void)
 {
 	nvlist_t *props;
 
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index e9db5340e..6b57f51ff 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -3878,7 +3878,7 @@ out:
  * Free buffers that were tagged for destruction.
  */
 static void
-l2arc_do_free_on_write()
+l2arc_do_free_on_write(void)
 {
 	list_t *buflist;
 	l2arc_data_free_t *df, *df_prev;
diff --git a/module/zfs/include/sys/dmu.h b/module/zfs/include/sys/dmu.h
index 07f5949eb..4580170db 100644
--- a/module/zfs/include/sys/dmu.h
+++ b/module/zfs/include/sys/dmu.h
@@ -529,8 +529,8 @@ int dmu_xuio_add(struct xuio *uio, struct arc_buf *abuf, offset_t off,
 int dmu_xuio_cnt(struct xuio *uio);
 struct arc_buf *dmu_xuio_arcbuf(struct xuio *uio, int i);
 void dmu_xuio_clear(struct xuio *uio, int i);
-void xuio_stat_wbuf_copied();
-void xuio_stat_wbuf_nocopy();
+void xuio_stat_wbuf_copied(void);
+void xuio_stat_wbuf_nocopy(void);
 
 extern int zfs_prefetch_disable;
 
diff --git a/module/zfs/include/sys/sa.h b/module/zfs/include/sys/sa.h
index bc89fa07d..c8b924771 100644
--- a/module/zfs/include/sys/sa.h
+++ b/module/zfs/include/sys/sa.h
@@ -147,8 +147,8 @@ int sa_replace_all_by_template(sa_handle_t *, sa_bulk_attr_t *,
 int sa_replace_all_by_template_locked(sa_handle_t *, sa_bulk_attr_t *,
     int, dmu_tx_t *);
 boolean_t sa_enabled(objset_t *);
-void sa_cache_init();
-void sa_cache_fini();
+void sa_cache_init(void);
+void sa_cache_fini(void);
 int sa_set_sa_object(objset_t *, uint64_t);
 int sa_hdrsize(void *);
 void sa_handle_lock(sa_handle_t *);
diff --git a/module/zfs/include/sys/spa.h b/module/zfs/include/sys/spa.h
index 7ebbbb2cd..52737ebc2 100644
--- a/module/zfs/include/sys/spa.h
+++ b/module/zfs/include/sys/spa.h
@@ -674,7 +674,7 @@ extern void vdev_cache_stat_fini(void);
 /* Initialization and termination */
 extern void spa_init(int flags);
 extern void spa_fini(void);
-extern void spa_boot_init();
+extern void spa_boot_init(void);
 
 /* properties */
 extern int spa_prop_set(spa_t *spa, nvlist_t *nvp);
diff --git a/module/zfs/include/sys/zfs_znode.h b/module/zfs/include/sys/zfs_znode.h
index 7fa7a0ae9..9d4b913ed 100644
--- a/module/zfs/include/sys/zfs_znode.h
+++ b/module/zfs/include/sys/zfs_znode.h
@@ -309,8 +309,8 @@ extern int	zfs_rezget(znode_t *);
 extern void	zfs_zinactive(znode_t *);
 extern void	zfs_znode_delete(znode_t *, dmu_tx_t *);
 extern void	zfs_znode_free(znode_t *);
-extern void	zfs_remove_op_tables();
-extern int	zfs_create_op_tables();
+extern void	zfs_remove_op_tables(void);
+extern int	zfs_create_op_tables(void);
 extern int	zfs_sync(vfs_t *vfsp, short flag, cred_t *cr);
 extern dev_t	zfs_cmpldev(uint64_t);
 extern int	zfs_get_zplprop(objset_t *os, zfs_prop_t prop, uint64_t *value);
diff --git a/module/zfs/include/sys/zil.h b/module/zfs/include/sys/zil.h
index a4c5575b2..45900c981 100644
--- a/module/zfs/include/sys/zil.h
+++ b/module/zfs/include/sys/zil.h
@@ -376,7 +376,7 @@ typedef int zil_parse_blk_func_t(zilog_t *zilog, blkptr_t *bp, void *arg,
     uint64_t txg);
 typedef int zil_parse_lr_func_t(zilog_t *zilog, lr_t *lr, void *arg,
     uint64_t txg);
-typedef int zil_replay_func_t();
+typedef int zil_replay_func_t(void *, char *, boolean_t);
 typedef int zil_get_data_t(void *arg, lr_write_t *lr, char *dbuf, zio_t *zio);
 
 extern int zil_parse(zilog_t *zilog, zil_parse_blk_func_t *parse_blk_func,
diff --git a/module/zfs/spa_history.c b/module/zfs/spa_history.c
index 212abae5b..a65f16bcc 100644
--- a/module/zfs/spa_history.c
+++ b/module/zfs/spa_history.c
@@ -175,7 +175,7 @@ spa_history_write(spa_t *spa, void *buf, uint64_t len, spa_history_phys_t *shpp,
 }
 
 static char *
-spa_history_zone()
+spa_history_zone(void)
 {
 #ifdef _KERNEL
 	return (curproc->p_zone->zone_name);
diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index 228ed1376..cd8a6c875 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -1516,7 +1516,7 @@ spa_busy(void)
 }
 
 void
-spa_boot_init()
+spa_boot_init(void)
 {
 	spa_config_load();
 }