diff --git a/mozjs/js/rust/src/rust.rs b/mozjs/js/rust/src/rust.rs
index d6967aa3db3..d6e44af72c0 100644
--- a/mozjs/js/rust/src/rust.rs
+++ b/mozjs/js/rust/src/rust.rs
@@ -482,6 +482,10 @@ impl Default for jsid {
     }
 }
 
+impl Default for JS::Value {
+    fn default() -> JS::Value { jsval::UndefinedValue() }
+}
+
 impl Default for JS::CompartmentOptions {
     fn default() -> Self { unsafe { ::std::mem::zeroed() } }
 }