diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index 2806356aa4..11a24e67c5 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -5346,7 +5346,7 @@ 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/include/sys/dmu.h b/module/zfs/include/sys/dmu.h
index 83932f467a..54115a08cb 100644
--- a/module/zfs/include/sys/dmu.h
+++ b/module/zfs/include/sys/dmu.h
@@ -528,8 +528,8 @@ 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 e9a96a0f95..176bb3a179 100644
--- a/module/zfs/include/sys/sa.h
+++ b/module/zfs/include/sys/sa.h
@@ -148,8 +148,8 @@ 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 *);