diff --git a/library/pkcs5.c b/library/pkcs5.c
index ac5945a..a6bc1b5 100644
--- a/library/pkcs5.c
+++ b/library/pkcs5.c
@@ -211,7 +211,6 @@
                               uint32_t key_length, unsigned char *output )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
-    int j;
     unsigned int i;
     unsigned char md1[MBEDTLS_MD_MAX_SIZE];
     unsigned char work[MBEDTLS_MD_MAX_SIZE];
@@ -263,8 +262,7 @@
 
             // U1 xor U2
             //
-            for( j = 0; j < md_size; j++ )
-                work[j] ^= md1[j];
+            mbedtls_xor( work, work, md1, md_size );
         }
 
         use_len = ( key_length < md_size ) ? key_length : md_size;
@@ -396,8 +394,7 @@
 
             // U1 xor U2
             //
-            for( j = 0; j < md_size; j++ )
-                work[j] ^= md1[j];
+            mbedtls_xor( work, work, md1, md_size );
         }
 
         use_len = ( key_length < md_size ) ? key_length : md_size;