diff --git a/include/mbedtls/x509.h b/include/mbedtls/x509.h
index c7b8cc4..c02c7c8 100644
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -318,7 +318,8 @@
                                              mbedtls_x509_buf *oid,
                                              mbedtls_x509_buf *val ),
                                void *check_ctx );
-int mbedtls_x509_memcasecmp( const void *s1, const void *s2, size_t len );
+int mbedtls_x509_memcasecmp( const void *s1, const void *s2,
+                             size_t len1, size_t lend2 );
 int mbedtls_x509_get_ext( unsigned char **p, const unsigned char *end,
                   mbedtls_x509_buf *ext, int tag );