diff --git a/include/mbedtls/x509.h b/include/mbedtls/x509.h
index 597053c7d..2afe4fa78 100644
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -293,7 +293,7 @@ int mbedtls_x509_get_ext( unsigned char **p, const unsigned char *end,
 int mbedtls_x509_sig_alg_gets( char *buf, size_t size, const mbedtls_x509_buf *sig_oid,
                        mbedtls_pk_type_t pk_alg, mbedtls_md_type_t md_alg,
                        const void *sig_opts );
-int mbedtls_x509_key_size_helper( char *buf, size_t size, const char *name );
+int mbedtls_x509_key_size_helper( char *buf, size_t buf_size, const char *name );
 int mbedtls_x509_string_to_names( mbedtls_asn1_named_data **head, const char *name );
 int mbedtls_x509_set_extension( mbedtls_asn1_named_data **head, const char *oid, size_t oid_len,
                         int critical, const unsigned char *val,
diff --git a/library/x509.c b/library/x509.c
index bd0d69a3c..2efa62f03 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -859,13 +859,13 @@ int mbedtls_x509_sig_alg_gets( char *buf, size_t size, const mbedtls_x509_buf *s
 /*
  * Helper for writing "RSA key size", "EC key size", etc
  */
-int mbedtls_x509_key_size_helper( char *buf, size_t size, const char *name )
+int mbedtls_x509_key_size_helper( char *buf, size_t buf_size, const char *name )
 {
     char *p = buf;
-    size_t n = size;
+    size_t n = buf_size;
     int ret;
 
-    if( strlen( name ) + sizeof( " key size" ) > size )
+    if( strlen( name ) + sizeof( " key size" ) > buf_size )
         return( ERR_BUF_TOO_SMALL );
 
     ret = mbedtls_snprintf( p, n, "%s key size", name );