diff --git a/zcash_test_vectors/hd_common.py b/zcash_test_vectors/hd_common.py
new file mode 100644
index 0000000..ddd4add
--- /dev/null
+++ b/zcash_test_vectors/hd_common.py
@@ -0,0 +1,7 @@
+# Common definitions for hierarchical derivation.
+
+ZCASH_MAIN_COINTYPE = 133
+
+def hardened(i):
+    assert 0 <= i and i < (1<<31)
+    return i + (1<<31)
diff --git a/zcash_test_vectors/sapling/zip32.py b/zcash_test_vectors/sapling/zip32.py
index bf22772..363fa0e 100755
--- a/zcash_test_vectors/sapling/zip32.py
+++ b/zcash_test_vectors/sapling/zip32.py
@@ -5,6 +5,8 @@ from hashlib import blake2b
 
 from .key_components import to_scalar, prf_expand, diversify_hash, DerivedAkNk, DerivedIvk
 from .generators import SPENDING_KEY_BASE, PROVING_KEY_BASE
+
+from ..hd_common import hardened
 from ..utils import i2leosp, i2lebsp, lebs2osp
 from ..ff1 import ff1_aes256_encrypt
 from ..output import render_args, render_tv, option, Some
@@ -219,11 +221,6 @@ class ExtendedFullViewingKey(DerivedIvk, ExtendedBase):
         return self.__class__(self.ak(), nk_internal, ovk_internal, dk_internal, self._c, self.depth(), self.parent_tag(), self._i)
 
 
-def hardened(i):
-    assert(i < (1<<31))
-    return i + (1<<31)
-
-
 def main():
     args = render_args()
 
diff --git a/zcash_test_vectors/unified_full_viewing_keys.py b/zcash_test_vectors/unified_full_viewing_keys.py
index d38cd20..e54b14e 100755
--- a/zcash_test_vectors/unified_full_viewing_keys.py
+++ b/zcash_test_vectors/unified_full_viewing_keys.py
@@ -10,9 +10,11 @@ from .output import render_args, render_tv, Some
 from .rand import Rand, randbytes
 from .orchard import key_components as orchard_key_components
 from .sapling import zip32 as sapling_zip32
+from .hd_common import ZCASH_MAIN_COINTYPE, hardened
 from .unified_encoding import encode_unified, decode_unified
 from .unified_encoding import P2PKH_ITEM, SAPLING_ITEM, ORCHARD_ITEM
 
+
 def main():
     args = render_args()
 
@@ -37,9 +39,9 @@ def main():
         has_s_key = rand.bool()
         if has_s_key:
             root_key = sapling_zip32.ExtendedSpendingKey.master(seed)
-            purpose_key = root_key.child(sapling_zip32.hardened(32))
-            coin_key = purpose_key.child(sapling_zip32.hardened(133))
-            account_key = coin_key.child(sapling_zip32.hardened(i))
+            purpose_key = root_key.child(hardened(32))
+            coin_key = purpose_key.child(hardened(ZCASH_MAIN_COINTYPE))
+            account_key = coin_key.child(hardened(i))
             sapling_fvk = account_key.to_extended_fvk()
 
             sapling_fvk_bytes = b"".join([
diff --git a/zcash_test_vectors/unified_incoming_viewing_keys.py b/zcash_test_vectors/unified_incoming_viewing_keys.py
index d4747bd..d19312b 100755
--- a/zcash_test_vectors/unified_incoming_viewing_keys.py
+++ b/zcash_test_vectors/unified_incoming_viewing_keys.py
@@ -10,9 +10,11 @@ from .output import render_args, render_tv, Some
 from .rand import Rand, randbytes
 from .orchard import key_components as orchard_key_components
 from .sapling import zip32 as sapling_zip32
+from .hd_common import ZCASH_MAIN_COINTYPE, hardened
 from .unified_encoding import encode_unified, decode_unified
 from .unified_encoding import P2PKH_ITEM, SAPLING_ITEM, ORCHARD_ITEM
 
+
 def main():
     args = render_args()
 
@@ -37,9 +39,9 @@ def main():
         has_s_key = rand.bool()
         if has_s_key:
             root_key = sapling_zip32.ExtendedSpendingKey.master(seed)
-            purpose_key = root_key.child(sapling_zip32.hardened(32))
-            coin_key = purpose_key.child(sapling_zip32.hardened(133))
-            account_key = coin_key.child(sapling_zip32.hardened(i))
+            purpose_key = root_key.child(hardened(32))
+            coin_key = purpose_key.child(hardened(ZCASH_MAIN_COINTYPE))
+            account_key = coin_key.child(hardened(i))
             sapling_dk = account_key.to_extended_fvk().dk()
             sapling_ivk = account_key.ivk()
             sapling_ivk_bytes = bytes(sapling_dk) + bytes(sapling_ivk)