diff --git a/nix-js/runtime-ts/src/operators.ts b/nix-js/runtime-ts/src/operators.ts
index 4f47724..75ab841 100644
--- a/nix-js/runtime-ts/src/operators.ts
+++ b/nix-js/runtime-ts/src/operators.ts
@@ -270,6 +270,12 @@ export const op = {
   update: (a: NixValue, b: NixValue): NixAttrs => {
     const mapA = forceAttrs(a);
     const mapB = forceAttrs(b);
+    if (mapA.size === 0) {
+      return mapB;
+    }
+    if (mapB.size === 0) {
+      return mapA;
+    }
     const result: NixAttrs = new Map(mapA);
     for (const [k, v] of mapB) {
       result.set(k, v);