diff --git a/client/hardnested/hardnested_bruteforce.c b/client/hardnested/hardnested_bruteforce.c
index 680f032a6..320c20f70 100644
--- a/client/hardnested/hardnested_bruteforce.c
+++ b/client/hardnested/hardnested_bruteforce.c
@@ -171,7 +171,7 @@ crack_states_thread(void *x)
                 __atomic_fetch_add(&found_bs_key, key, __ATOMIC_SEQ_CST);
 
                 char progress_text[80];
-                char keystr[18];
+                char keystr[19];
                 sprintf(keystr, "%012" PRIx64 "  ", key);
                 sprintf(progress_text, "Brute force phase completed. Key found: " _YELLOW_( % s), keystr);
                 hardnested_print_progress(thread_arg->num_acquired_nonces, progress_text, 0.0, 0);