diff --git a/src/keys.rs b/src/keys.rs
index ad218b15..5572024c 100644
--- a/src/keys.rs
+++ b/src/keys.rs
@@ -38,6 +38,14 @@ const ZIP32_PURPOSE: u32 = 32;
 #[derive(Debug, Copy, Clone)]
 pub struct SpendingKey([u8; 32]);
 
+/// An internal spending key, derived from a spending key.
+///
+/// Specified in [ZIP32][orchardinternalspendingkey].
+///
+/// [orchardinternalspendingkey]: https://zips.z.cash/zip-0032#orchard-internal-key-derivation
+#[derive(Debug, Copy, Clone)]
+pub struct InternalSpendingKey([u8; 32]);
+
 impl ConstantTimeEq for SpendingKey {
     fn ct_eq(&self, other: &Self) -> Choice {
         self.to_bytes().ct_eq(other.to_bytes())
@@ -96,6 +104,11 @@ impl SpendingKey {
         ];
         ExtendedSpendingKey::from_path(seed, path).map(|esk| esk.sk())
     }
+
+    /// Derives an internal spending key from a spending key,
+    pub fn derive_internal(&self) -> InternalSpendingKey {
+        InternalSpendingKey(self.0)
+    }
 }
 
 /// A spend authorizing key, used to create spend authorization signatures.
@@ -256,6 +269,12 @@ impl From<&SpendingKey> for CommitIvkRandomness {
     }
 }
 
+impl From<&InternalSpendingKey> for CommitIvkRandomness {
+    fn from(sk: &InternalSpendingKey) -> Self {
+        CommitIvkRandomness(to_scalar(PrfExpand::OrchardRivkInternal.expand(&sk.0)))
+    }
+}
+
 impl CommitIvkRandomness {
     pub(crate) fn inner(&self) -> pallas::Scalar {
         self.0