Stop warning about use of *printf() without a format.
diff --git a/apps/s_client.c b/apps/s_client.c
index dcc289b..5f09c31 100644
--- a/apps/s_client.c
+++ b/apps/s_client.c
@@ -237,7 +237,7 @@
 		BIO_printf(bio_c_out, "Received PSK identity hint '%s'\n", hint);
 
 	/* lookup PSK identity and PSK key based on the given identity hint here */
-	ret = BIO_snprintf(identity, max_identity_len, psk_identity);
+	ret = BIO_snprintf(identity, max_identity_len, "%s", psk_identity);
 	if (ret < 0 || (unsigned int)ret > max_identity_len)
 		goto out_err;
 	if (c_debug)