diff --git a/pstree.c b/pstree.c
index cddca5a63..d68d8faeb 100644
--- a/pstree.c
+++ b/pstree.c
@@ -544,6 +544,7 @@ set_mask:
 		}
 	}
 
+	pr_debug("NS mask to use %lx\n", current_ns_mask);
 	return 0;
 }