diff --git a/src/prolog/lib/crypto.pl b/src/prolog/lib/crypto.pl
index b93a9cff..909127d4 100644
--- a/src/prolog/lib/crypto.pl
+++ b/src/prolog/lib/crypto.pl
@@ -184,8 +184,7 @@ crypto_random_byte(B) :- '$crypto_random_byte'(B).
 
 crypto_data_hash(Data0, Hash, Options0) :-
         must_be(list, Options0),
-        option(encoding(Encoding), Options0, utf8),
-        encoding_bytes(Encoding, Data0, Data),
+        options_data_bytes(Options0, Data0, Data),
         functor_hash_options(algorithm, A, Options0, _),
         (   hash_algorithm(A) -> true
         ;   domain_error(hash_algorithm, A, crypto_data_hash/3)
@@ -193,6 +192,10 @@ crypto_data_hash(Data0, Hash, Options0) :-
         '$crypto_data_hash'(Data, HashBytes, A),
         hex_bytes(Hash, HashBytes).
 
+options_data_bytes(Options, Data, Bytes) :-
+        option(encoding(Encoding), Options, utf8),
+        must_be(atom, Encoding),
+        encoding_bytes(Encoding, Data, Bytes).
 
 default_hash(sha256).
 
@@ -250,8 +253,9 @@ hash_algorithm(sha512_256).
 
 crypto_data_hkdf(Data0, L, Bytes, Options0) :-
         functor_hash_options(algorithm, Algorithm, Options0, Options),
-        option(encoding(Encoding), Options, utf8),
-        encoding_bytes(Encoding, Data0, Data),
+        must_be(integer, L),
+        L >= 0,
+        options_data_bytes(Options, Data0, Data),
         option(salt(SaltBytes), Options, []),
         must_be_bytes(SaltBytes, crypto_data_hkdf/4),
         option(info(Info0), Options, []),
@@ -259,6 +263,10 @@ crypto_data_hkdf(Data0, L, Bytes, Options0) :-
         '$crypto_data_hkdf'(Data, SaltBytes, Info, Algorithm, L, Bytes).
 
 option(What, Options, Default) :-
+        (   member(V, Options), var(V) ->
+            instantiation_error(option/3)
+        ;   true
+        ),
         (   member(What, Options) -> true
         ;   What =.. [_,Default]
         ).
@@ -379,7 +387,7 @@ crypto_password_hash(Password0, Hash, Options) :-
         Algorithm = 'pbkdf2-sha512', % current default and only option
         option(algorithm(Algorithm), Options, Algorithm),
         (   member(salt(SaltBytes), Options) ->
-            true
+            must_be_bytes(SaltBytes, crypto_password_hash/2)
         ;   crypto_n_random_bytes(16, SaltBytes)
         ),
         '$crypto_password_hash'(Password, SaltBytes, Iterations, HashBytes),
@@ -531,8 +539,7 @@ bytes_base64_([A,B,C|Ls]) --> [W,X,Y,Z],
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
 crypto_data_encrypt(PlainText0, Algorithm, Key, IV, CipherText, Options) :-
-        option(encoding(Encoding), Options, utf8),
-        encoding_bytes(Encoding, PlainText0, PlainText),
+        options_data_bytes(Options, PlainText0, PlainText),
         option(tag(Tag), Options, _),
         (   nonvar(Tag) ->
             must_be_bytes(Tag, crypto_data_encrypt/6)
@@ -580,7 +587,7 @@ crypto_data_decrypt(CipherText0, Algorithm, Key, IV, PlainText, Options) :-
         must_be_bytes(Key, crypto_data_decrypt/6),
         must_be_bytes(IV, crypto_data_decrypt/6),
         must_be(atom, Algorithm),
-        option(encoding(Encoding), Options, utf8),
+        encoding_options(Encoding, Options),
         must_be(list, CipherText0),
         encoding_bytes(octet, CipherText0, CipherText1),
         append(CipherText1, Tag, CipherText),
@@ -590,19 +597,19 @@ crypto_data_decrypt(CipherText0, Algorithm, Key, IV, PlainText, Options) :-
         '$crypto_data_decrypt'(CipherText, Key, IV, Encoding, PlainText).
 
 encoding_bytes(octet, Bs0, Bs) :-
+        must_be(list, Bs0),
         (   maplist(integer, Bs0) ->
             Bs0 = Bs
         ;   maplist(char_code, Bs0, Bs)
         ),
         must_be_bytes(Bs, crypto_encoding).
 encoding_bytes(utf8, Cs, Bs) :-
+        must_be(list, Cs),
         (   maplist(atom, Cs) ->
             chars_bytes_(Cs, Bs, crypto_encoding)
         ;   domain_error(encryption_encoding, Cs, crypto)
         ).
 
-char_code(Char, Code) :- atom_codes(Char, [Code]).
-
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Modular multiplicative inverse.
 
diff --git a/src/prolog/machine/system_calls.rs b/src/prolog/machine/system_calls.rs
index 8281259e..9554badb 100644
--- a/src/prolog/machine/system_calls.rs
+++ b/src/prolog/machine/system_calls.rs
@@ -5275,7 +5275,10 @@ impl MachineState {
                              let salt = hkdf::Salt::new(digest_alg, &salt);
                              let mut bytes : Vec<u8> = Vec::new();
                              bytes.resize(length, 0);
-                             salt.extract(&data).expand(&[&info[..]], MyKey(length)).unwrap().fill(&mut bytes).unwrap();
+                             match salt.extract(&data).expand(&[&info[..]], MyKey(length)) {
+                                 Ok(r) => { r.fill(&mut bytes).unwrap(); }
+                                 _ => { self.fail = true; return Ok(()); }
+                             }
 
                              Addr::HeapCell(self.heap.to_list(bytes.iter().map(|b| HeapCellValue::Integer(Rc::new(Integer::from(*b))))))
                         };
@@ -5294,7 +5297,10 @@ impl MachineState {
                             u64::try_from(n).unwrap()
                         }
                         Ok(Number::Integer(n)) => {
-                            n.to_u64().unwrap()
+                            match n.to_u64() {
+                                Some(i) => { i }
+                                None => { self.fail = true; return Ok(()); }
+                            }
                         }
                         _ => {
                             unreachable!()