diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
index 354e4d6746c3..cda427a0dab7 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
@@ -203,6 +203,7 @@ int zfs_arc_grow_retry = 0;
 int zfs_arc_shrink_shift = 0;
 int zfs_arc_p_min_shift = 0;
 int zfs_disable_dup_eviction = 0;
+uint64_t zfs_arc_average_blocksize = 8 * 1024; /* 8KB */
 
 TUNABLE_QUAD("vfs.zfs.arc_meta_limit", &zfs_arc_meta_limit);
 SYSCTL_DECL(_vfs_zfs);
@@ -210,6 +211,9 @@ SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_max, CTLFLAG_RDTUN, &zfs_arc_max, 0,
     "Maximum ARC size");
 SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_min, CTLFLAG_RDTUN, &zfs_arc_min, 0,
     "Minimum ARC size");
+SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_average_blocksize, CTLFLAG_RDTUN,
+    &zfs_arc_average_blocksize, 0,
+    "ARC average blocksize");
 
 /*
  * Note that buffers can be in one of 6 states:
@@ -1054,10 +1058,11 @@ buf_init(void)
 
 	/*
 	 * The hash table is big enough to fill all of physical memory
-	 * with an average 64K block size.  The table will take up
-	 * totalmem*sizeof(void*)/64K (eg. 128KB/GB with 8-byte pointers).
+	 * with an average block size of zfs_arc_average_blocksize (default 8K).
+	 * By default, the table will take up
+	 * totalmem * sizeof(void*) / 8K (1MB per GB with 8-byte pointers).
 	 */
-	while (hsize * 65536 < (uint64_t)physmem * PAGESIZE)
+	while (hsize * zfs_arc_average_blocksize < (uint64_t)physmem * PAGESIZE)
 		hsize <<= 1;
 retry:
 	buf_hash_table.ht_mask = hsize - 1;