diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index b77fc7b631..45fb5ed193 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -296,7 +296,7 @@ int mbedtls_ssl_tls13_evolve_secret(
     int ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
     size_t hlen, ilen;
     unsigned char tmp_secret[ MBEDTLS_MD_MAX_SIZE ] = { 0 };
-    unsigned char tmp_input [ MBEDTLS_MD_MAX_SIZE ] = { 0 };
+    unsigned char tmp_input [ MBEDTLS_ECP_MAX_BYTES ] = { 0 };
 
     const mbedtls_md_info_t *md_info;
     md_info = mbedtls_md_info_from_type( hash_alg );