diff --git a/frontend/src/lib/format.test.ts b/frontend/src/lib/format.test.ts
index 7b738568..e9d8dcb4 100644
--- a/frontend/src/lib/format.test.ts
+++ b/frontend/src/lib/format.test.ts
@@ -121,9 +121,11 @@ describe("formatRuntime", () => {
     [0, ""], // nothing to show — the call sites suppress their separator on the empty string
     [1, "1s"],
     [45, "45s"], // one Short: the regression case
+    [45.7, "45s"], // truncates, so the seconds tier cannot overstate either
     [59, "59s"], // last second before the minute tier
     [60, "1m"],
     [90, "1m"], // floors, never rounds up — a total must not overstate
+    [90.9, "1m"],
     [3599, "59m"],
     [3600, "1h 0m"], // the zero minutes stay: "1h" alone reads as an approximation
     [5025, "1h 23m"],