diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index e8f351dfc509d90e1c9b20d237c0db002f767bb8..9d9e193a8c50d7e811c348e000e07a06c56ba1ee 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -76,7 +76,8 @@ extern "C" {
 
 # define SSL_MIN_RSA_MODULUS_LENGTH_IN_BYTES     (512/8)
 # define SSL_MAX_KEY_ARG_LENGTH                  8
-# define SSL_MAX_MASTER_KEY_LENGTH               64
+# define SSL_MAX_MASTER_KEY_LENGTH               48
+# define TLS13_MAX_RESUMPTION_MASTER_LENGTH      64
 
 /* The maximum number of encrypt/decrypt pipelines we can support */
 # define SSL_MAX_PIPELINES  32
diff --git a/ssl/ssl_asn1.c b/ssl/ssl_asn1.c
index 568f41ff5b016f36f298b59a6cabe718b22d5f40..73ba78dbe573f0186f10df17d7ffcbef0d23134b 100644
--- a/ssl/ssl_asn1.c
+++ b/ssl/ssl_asn1.c
@@ -294,7 +294,7 @@ SSL_SESSION *d2i_SSL_SESSION(SSL_SESSION **a, const unsigned char **pp,
         goto err;
 
     if (!ssl_session_memcpy(ret->master_key, &tmpl,
-                            as->master_key, SSL_MAX_MASTER_KEY_LENGTH))
+                            as->master_key, TLS13_MAX_RESUMPTION_MASTER_LENGTH))
         goto err;
 
     ret->master_key_length = tmpl;
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index e74c0f480a82465c72699f88afe5b98b0bc01b12..f95b4660a70ae13b0108045efc1381b98b12dddd 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -515,7 +515,7 @@ struct ssl_session_st {
      * For <=TLS1.2 this is the master_key. For TLS1.3 this is the resumption
      * master secret
      */
-    unsigned char master_key[SSL_MAX_MASTER_KEY_LENGTH];
+    unsigned char master_key[TLS13_MAX_RESUMPTION_MASTER_LENGTH];
     /* session_id - valid? */
     size_t session_id_length;
     unsigned char session_id[SSL_MAX_SSL_SESSION_ID_LENGTH];