diff --git a/include/polarssl/aes.h b/include/polarssl/aes.h
index 7404e4e..efc13da 100644
--- a/include/polarssl/aes.h
+++ b/include/polarssl/aes.h
@@ -124,7 +124,7 @@
 int aes_crypt_cfb128( aes_context *ctx,
                        int mode,
                        size_t length,
-                       int *iv_off,
+                       size_t *iv_off,
                        unsigned char iv[16],
                        const unsigned char *input,
                        unsigned char *output );
@@ -147,8 +147,8 @@
  * \return         0 if successful
  */
 int aes_crypt_ctr( aes_context *ctx,
-                       int length,
-                       int *nc_off,
+                       size_t length,
+                       size_t *nc_off,
                        unsigned char nonce_counter[16],
                        unsigned char stream_block[16],
                        const unsigned char *input,