diff --git a/core/src/services/mongodb/backend.rs b/core/src/services/mongodb/backend.rs
index 1224bfda97d8..cafed8fb3efb 100644
--- a/core/src/services/mongodb/backend.rs
+++ b/core/src/services/mongodb/backend.rs
@@ -108,7 +108,6 @@ impl MongodbBuilder {
     pub fn key_field(&mut self, key_field: &str) -> &mut Self {
         if !key_field.is_empty() {
             self.key_field = Some(key_field.to_string());
-            self.key_field = Some(key_field.to_string());
         }
         self
     }