diff --git a/src/modules/commander/calibration_routines.cpp b/src/modules/commander/calibration_routines.cpp
index 88134082f9..b351ac1bd3 100644
--- a/src/modules/commander/calibration_routines.cpp
+++ b/src/modules/commander/calibration_routines.cpp
@@ -452,8 +452,8 @@ calibrate_return calibrate_from_orientation(orb_advert_t *mavlink_log_pub,
 
 		for (unsigned int cur_orientation=0; cur_orientation<detect_orientation_side_count; cur_orientation++) {
 			if (!side_data_collected[cur_orientation]) {
-				strncat(pendingStr, " ", sizeof(pendingStr));
-				strncat(pendingStr, detect_orientation_str((enum detect_orientation_return)cur_orientation), sizeof(pendingStr));
+				strncat(pendingStr, " ", sizeof(pendingStr) - 1);
+				strncat(pendingStr, detect_orientation_str((enum detect_orientation_return)cur_orientation), sizeof(pendingStr) - 1);
 			}
 		}
 		calibration_log_info(mavlink_log_pub, "[cal] pending:%s", pendingStr);