Const fix.
diff --git a/apps/s_client.c b/apps/s_client.c
index 6a4b2da..9efea79 100644
--- a/apps/s_client.c
+++ b/apps/s_client.c
@@ -227,7 +227,7 @@
 
 static unsigned char *generated_supp_data = NULL;
 
-static unsigned char *most_recent_supplemental_data = NULL;
+static const unsigned char *most_recent_supplemental_data = NULL;
 static size_t most_recent_supplemental_data_length = 0;
 
 static int server_provided_server_authz = 0;