diff --git a/package.json b/package.json
index 3d1d136..6831311 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
 	"scripts": {
 		"test": "mocha",
 		"build": "esbuild src/browser.ts --bundle --minify --sourcemap --target=firefox120 --outfile=public/bundle.js",
+		"watch": "npm run build -- --watch",
 		"prepare": "npm run build",
 		"clean-coverage": "rm -rf coverage .nyc_output .xunit",
 		"coverage": "npm run clean-coverage && nyc mocha",
diff --git a/src/index.ts b/src/index.ts
index 978ae1d..d49b709 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -35,9 +35,15 @@ function parseTimestamp(s: string): number {
 
 function toTimestamp(n: number): string {
 	n = Math.floor(n);
-	return `${Math.floor(n / 60)
-		.toString()
-		.padStart(2, "0")}:${(n % 60).toString().padStart(2, "0")}`;
+	let result: number[] = [];
+	while (n / 60 > 0) {
+		result.push(n % 60);
+		n = Math.floor(n / 60);
+	}
+	return result
+		.map((n, i) => (i >= 2 ? n.toString() : n.toString().padStart(2, "0")))
+		.reverse()
+		.join(":");
 }
 
 export function parse_youtube(content: string): Timestamp[] {