diff --git a/programs/ssl/ssl_server.c b/programs/ssl/ssl_server.c
index 3e1d9a4..9668cf9 100644
--- a/programs/ssl/ssl_server.c
+++ b/programs/ssl/ssl_server.c
@@ -309,7 +309,7 @@
                     break;
 
                 default:
-                    mbedtls_printf( " mbedtls_ssl_read returned -0x%x\n", -ret );
+                    mbedtls_printf( " mbedtls_ssl_read returned -0x%x\n", (unsigned int) -ret );
                     break;
             }