diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 933d3d9..5a4574d 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -1590,8 +1590,8 @@
 #if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
     if( auth_done == 0 )
     {
-        unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
-        unsigned char mac_peer[MBEDTLS_SSL_MAC_ADD];
+        unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD] = { 0 };
+        unsigned char mac_peer[MBEDTLS_SSL_MAC_ADD] = { 0 };
 
         /* If the initial value of padlen was such that
          * data_len < maclen + padlen + 1, then padlen