diff --git a/crates/tor-llcrypto/src/pk/keymanip.rs b/crates/tor-llcrypto/src/pk/keymanip.rs
index 7c5020c8b..960f8807c 100644
--- a/crates/tor-llcrypto/src/pk/keymanip.rs
+++ b/crates/tor-llcrypto/src/pk/keymanip.rs
@@ -112,6 +112,11 @@ pub fn convert_curve25519_to_ed25519_private(
 ///
 /// Note: Using the same keypair for multiple purposes (such as key-exchange and signing) is
 /// considered bad practice. Don't use this function unless you know what you're doing.
+///
+/// It's important to note that converting a private key from ed25519 -> curve25519 -> ed25519 will
+/// yield an [`ExpandedKeypair`](pk::ed25519::ExpandedKeypair) that is _not_ identical to the
+/// expanded version of the original [`Keypair`](pk::ed25519::Keypair): the lower halves (the keys) of
+/// the expanded key pairs will be the same, but their upper halves (the nonces) will be different.
 #[cfg(any(test, feature = "keymgr"))]
 pub fn convert_ed25519_to_curve25519_private(
     keypair: &pk::ed25519::Keypair,