diff --git a/src/ui/window.vala b/src/ui/window.vala
index 4681694..b8763e8 100644
--- a/src/ui/window.vala
+++ b/src/ui/window.vala
@@ -135,6 +135,10 @@ class Ui.Window : Adw.ApplicationWindow {
     }
 
     [GtkCallback] private string format_timestamp (int64 ns) {
+        if (ns == 1) {
+            // treat 1 nanosecond as a sentinel value
+            return "-";
+        }
         int64 ms = ns / 1000000;
         int s = (int) (ms / 1000);
         return "%02d:%02d".printf (s/60, s%60);