diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index b41d385..807fb18 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -633,7 +633,7 @@
     /* Remember the client asked us to send a new ticket */
     ssl->handshake->new_session_ticket = 1;
 
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket length: %zu", len ) );
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "ticket length: %" MBEDTLS_PRINTF_SIZET, len ) );
 
     if( len == 0 )
         return( 0 );
@@ -2826,7 +2826,8 @@
     *p++ = (unsigned char)( t >>  8 );
     *p++ = (unsigned char)( t       );
 
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, current time: %lld", (long long) t ) );
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, current time: %" MBEDTLS_PRINTF_LONGLONG,
+                                (long long) t ) );
 #else
     if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, p, 4 ) ) != 0 )
         return( ret );
@@ -2914,7 +2915,7 @@
     memcpy( p, ssl->session_negotiate->id, ssl->session_negotiate->id_len );
     p += ssl->session_negotiate->id_len;
 
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, session id len.: %zu", n ) );
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, session id len.: %" MBEDTLS_PRINTF_SIZET, n ) );
     MBEDTLS_SSL_DEBUG_BUF( 3,   "server hello, session id", buf + 39, n );
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "%s session has been resumed",
                    ssl->handshake->resume ? "a" : "no" ) );
@@ -2995,7 +2996,8 @@
     ext_len += olen;
 #endif
 
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, total extension length: %zu", ext_len ) );
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, total extension length: %" MBEDTLS_PRINTF_SIZET,
+                                ext_len ) );
 
     if( ext_len > 0 )
     {