diff --git a/martian/src/mro.rs b/martian/src/mro.rs
index 266dfae173..ded7d81db4 100644
--- a/martian/src/mro.rs
+++ b/martian/src/mro.rs
@@ -622,7 +622,7 @@ macro_rules! mro_using {
                     return Ok(());
                 }
                 $(
-                    if let Some(ref $property) = self.$property {
+                    if let Some($property) = self.$property.clone() {
                         writeln!(
                             f,
                             "{blank:indent$}{key:<width$} = {value},",