diff --git a/nix-js/runtime-ts/src/helpers.ts b/nix-js/runtime-ts/src/helpers.ts
index b6e8807..fca9d92 100644
--- a/nix-js/runtime-ts/src/helpers.ts
+++ b/nix-js/runtime-ts/src/helpers.ts
@@ -242,17 +242,20 @@ export const selectWithDefault = (
   }
 };
 
-function selectWithDefault_impl(obj: NixValue, attrpath: NixValue[], default_val: NixValue): NixValue {
-  let attrs = forceAttrs(obj);
+function selectWithDefault_impl(obj: NixValue, attrpath: NixValue[], defaultVal: NixValue): NixValue {
+  let attrs = force(obj);
+  if (!isAttrs(attrs)) {
+    return defaultVal;
+  }
 
   for (const attr of attrpath.slice(0, -1)) {
     const key = forceStringValue(attr);
     if (!(key in attrs)) {
-      return default_val;
+      return defaultVal;
     }
     const cur = force(attrs[key]);
     if (!isAttrs(cur)) {
-      return default_val;
+      return defaultVal;
     }
     attrs = cur;
   }
@@ -261,7 +264,7 @@ function selectWithDefault_impl(obj: NixValue, attrpath: NixValue[], default_val
   if (last in attrs) {
     return attrs[last];
   }
-  return default_val;
+  return defaultVal;
 }
 
 export const hasAttr = (obj: NixValue, attrpath: NixValue[]): NixBool => {