diff --git a/packages/coding-agent/test/status-line-overflow.test.ts b/packages/coding-agent/test/status-line-overflow.test.ts
index 77a1a97df..18c2779e0 100644
--- a/packages/coding-agent/test/status-line-overflow.test.ts
+++ b/packages/coding-agent/test/status-line-overflow.test.ts
@@ -144,10 +144,13 @@ describe("status line session accent", () => {
 	}
 
 	// Computed lazily: `theme` is assigned by initTheme() in beforeAll, after module evaluation.
-	const accentAnsi = () =>
-		getSessionAccentAnsi(
+	const accentAnsi = (): string => {
+		const ansi = getSessionAccentAnsi(
 			getSessionAccentHex("Named session", theme.getMajorThemeColorHexes(), theme.accentSurfaceLuminance),
 		);
+		if (!ansi) throw new Error("expected a session accent ANSI sequence for the test theme");
+		return ansi;
+	};
 
 	it("paints the gap with the session accent when enabled", () => {
 		const ansi = accentAnsi();