diff --git a/src/standalone/stubs/moment-duration-format.js b/src/standalone/stubs/moment-duration-format.js
index 2f118bc..9602707 100644
--- a/src/standalone/stubs/moment-duration-format.js
+++ b/src/standalone/stubs/moment-duration-format.js
@@ -1 +1,22 @@
-// Stub for moment-duration-format (side-effect-only import, not needed in standalone)
+// Stub for moment-duration-format
+// The real package extends moment.duration.fn with a .format() method.
+// We provide a minimal implementation so that standalone builds don't crash.
+import moment from "moment";
+
+if (moment.duration.fn && !moment.duration.fn.format) {
+    moment.duration.fn.format = function (template) {
+        const totalSeconds = Math.abs(this.asSeconds());
+        const hours = Math.floor(totalSeconds / 3600);
+        const minutes = Math.floor((totalSeconds % 3600) / 60);
+        const seconds = Math.floor(totalSeconds % 60);
+        if (template === "d[d] hh:mm:ss" || template === "hh:mm:ss") {
+            const days = Math.floor(totalSeconds / 86400);
+            const remainingHours = Math.floor((totalSeconds % 86400) / 3600);
+            if (days > 0) {
+                return `${days}d ${String(remainingHours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}`;
+            }
+            return `${String(hours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}`;
+        }
+        return `${String(hours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}`;
+    };
+}