diff --git a/src/main.rs b/src/main.rs
index 1582e8c..0bf0dcb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -135,7 +135,9 @@ impl Serialize for Env {
             name_id_map.reserve(self.output_names.len());
             let mut id = 0;
             for (_, value) in &self.output_names {
-                name_id_map.insert(value, id);
+                if !name_id_map.contains_key(value.as_str()) {
+                    name_id_map.insert(value, id);
+                }
                 id += 1;
             }
             state.serialize_field("gtk_ids", &name_id_map)?;