diff --git a/secp256k1-sys/src/lib.rs b/secp256k1-sys/src/lib.rs
index df0c3b5e4..060ea3303 100644
--- a/secp256k1-sys/src/lib.rs
+++ b/secp256k1-sys/src/lib.rs
@@ -63,7 +63,7 @@ pub type NonceFn = unsafe extern "C" fn(nonce32: *mut c_uchar,
                                         algo16: *const c_uchar,
                                         data: *mut c_void,
                                         attempt: c_uint,
-);
+) -> c_int;
 
 /// Hash function to use to post-process an ECDH point to get
 /// a shared secret.
@@ -491,13 +491,6 @@ mod fuzz_dummy {
         1
     }
 
-    // TODO secp256k1_context_set_illegal_callback
-    // TODO secp256k1_context_set_error_callback
-    // (Actually, I don't really want these exposed; if either of these
-    // are ever triggered it indicates a bug in rust-secp256k1, since
-    // one goal is to use Rust's type system to eliminate all possible
-    // bad inputs.)
-
     // Pubkeys
     /// Parse 33/65 byte pubkey into PublicKey, losing compressed information
     pub unsafe fn secp256k1_ec_pubkey_parse(cx: *const Context, pk: *mut PublicKey,