diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index f9dea9c..0d3623e 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -2100,7 +2100,7 @@
     len = (*p)[0] << 8 | (*p)[1];
     *p += 2;
 
-    if( end - (*p) < len )
+    if( end - (*p) < (int) len )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message "
                                     "(psk_identity_hint length)" ) );