diff --git a/tor-proto/src/crypto/handshake/ntor.rs b/tor-proto/src/crypto/handshake/ntor.rs
index e8a48569b..210107904 100644
--- a/tor-proto/src/crypto/handshake/ntor.rs
+++ b/tor-proto/src/crypto/handshake/ntor.rs
@@ -35,7 +35,7 @@ pub struct NtorSecretKey {
 
 use subtle::{Choice, ConstantTimeEq};
 impl NtorSecretKey {
-    fn matches_pk(&self, pk: PublicKey) -> Choice {
+    fn matches_pk(&self, pk: &PublicKey) -> Choice {
         self.pk.pk.as_bytes().ct_eq(pk.as_bytes())
     }
 }
@@ -222,7 +222,7 @@ where
     let my_key: PublicKey = cur.extract()?;
     let their_pk: PublicKey = cur.extract()?;
 
-    let keypair = ct::lookup(&my_key, keys, |a, b| b.matches_pk(*a));
+    let keypair = ct::lookup(keys, |key| key.matches_pk(&my_key));
     let keypair = match keypair {
         Some(k) => k,
         None => return Err(Error::MissingKey),
diff --git a/tor-proto/src/util/ct.rs b/tor-proto/src/util/ct.rs
index f6d643566..9c38fb016 100644
--- a/tor-proto/src/util/ct.rs
+++ b/tor-proto/src/util/ct.rs
@@ -4,8 +4,8 @@ use subtle::*;
 /// Try to find an item in a slice without leaking where and whether the
 /// item was found.
 ///
-/// If there is any item `x` in the `array` for which `matches(item,
-/// x)` is true, this function will return a reference to one such
+/// If there is any item `x` in the `array` for which `matches(x)`
+/// is true, this function will return a reference to one such
 /// item.  (We don't specify which.)
 ///
 /// Otherwise, this function returns none.
@@ -15,12 +15,9 @@ use subtle::*;
 ///
 /// Note that this doesn't necessarily do a constant-time comparison,
 /// and that it is not constant-time for found/not-found case.
-///
-/// TODO: the item 'item' should really be part of the 'matches' closure.
-pub fn lookup<'a, T, U, F>(item: &T, array: &'a [U], matches: F) -> Option<&'a U>
+pub fn lookup<T, F>(array: &[T], matches: F) -> Option<&T>
 where
-    F: Fn(&T, &U) -> Choice,
-    T: ?Sized,
+    F: Fn(&T) -> Choice,
 {
     // ConditionallySelectable isn't implemented for usize, so we need
     // to use u64.
@@ -28,7 +25,7 @@ where
     let mut found: Choice = 0.into();
 
     for (i, x) in array.iter().enumerate() {
-        let equal = matches(item, x);
+        let equal = matches(x);
         idx.conditional_assign(&(i as u64), equal);
         found.conditional_assign(&equal, equal)
     }