diff --git a/crypto_sign/rainbowIa-classic/clean/utils_hash.c b/crypto_sign/rainbowIa-classic/clean/utils_hash.c
index 8c9e3aab..358a20f7 100644
--- a/crypto_sign/rainbowIa-classic/clean/utils_hash.c
+++ b/crypto_sign/rainbowIa-classic/clean/utils_hash.c
@@ -9,7 +9,7 @@
 #include "utils_hash.h"
 
 static inline
-int _hash( unsigned char *digest, const unsigned char *m, unsigned long long mlen ) {
+int _hash( unsigned char *digest, const unsigned char *m, size_t mlen ) {
 //    #if 32 == _HASH_LEN
     sha256(digest, m, mlen);
 //    #elif 48 == _HASH_LEN
@@ -23,20 +23,20 @@ int _hash( unsigned char *digest, const unsigned char *m, unsigned long long mle
 }
 
 static inline
-int expand_hash( unsigned char *digest, unsigned n_digest, const unsigned char *hash ) {
+int expand_hash(unsigned char *digest, size_t n_digest, const unsigned char *hash) {
     if ( _HASH_LEN >= n_digest ) {
-        for (unsigned i = 0; i < n_digest; i++) {
+        for (size_t i = 0; i < n_digest; i++) {
             digest[i] = hash[i];
         }
         return 0;
     }
-    for (unsigned i = 0; i < _HASH_LEN; i++) {
+    for (size_t i = 0; i < _HASH_LEN; i++) {
         digest[i] = hash[i];
     }
     n_digest -= _HASH_LEN;
 
 
-    while ( _HASH_LEN <= n_digest ) {
+    while (_HASH_LEN <= n_digest ) {
         _hash( digest + _HASH_LEN, digest, _HASH_LEN );
 
         n_digest -= _HASH_LEN;
@@ -45,18 +45,20 @@ int expand_hash( unsigned char *digest, unsigned n_digest, const unsigned char *
     unsigned char temp[_HASH_LEN];
     if ( n_digest ) {
         _hash( temp, digest, _HASH_LEN );
-        for (unsigned i = 0; i < n_digest; i++) {
+        for (size_t i = 0; i < n_digest; i++) {
             digest[_HASH_LEN + i] = temp[i];
         }
     }
     return 0;
 }
 
-int PQCLEAN_RAINBOWIACLASSIC_CLEAN_hash_msg( unsigned char *digest, unsigned len_digest, const unsigned char *m, unsigned long long mlen ) {
+int PQCLEAN_RAINBOWIACLASSIC_CLEAN_hash_msg(unsigned char *digest,
+        size_t len_digest,
+        const unsigned char *m,
+        size_t mlen) {
     unsigned char buf[_HASH_LEN];
-    _hash( buf, m, mlen );
-
-    return expand_hash( digest, len_digest, buf );
+    _hash(buf, m, mlen);
+    return expand_hash(digest, len_digest, buf);
 }
 
 
diff --git a/crypto_sign/rainbowIa-classic/clean/utils_hash.h b/crypto_sign/rainbowIa-classic/clean/utils_hash.h
index ba234866..9c011a2e 100644
--- a/crypto_sign/rainbowIa-classic/clean/utils_hash.h
+++ b/crypto_sign/rainbowIa-classic/clean/utils_hash.h
@@ -7,8 +7,9 @@
 
 // for the definition of _HASH_LEN.
 #include "hash_len_config.h"
+#include <stddef.h>
 
-int PQCLEAN_RAINBOWIACLASSIC_CLEAN_hash_msg( unsigned char *digest, unsigned len_digest, const unsigned char *m, unsigned long long mlen );
+int PQCLEAN_RAINBOWIACLASSIC_CLEAN_hash_msg( unsigned char *digest, size_t len_digest, const unsigned char *m, size_t mlen );