diff --git a/src/error.rs b/src/error.rs
index fbc3e2f3..6c98304a 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -216,7 +216,7 @@ pub enum ParseRequestError {
 
     /// The request's files map was invalid.
     #[error("Invalid files map: {0}")]
-    InvalidFilesMap(serde_json::Error),
+    InvalidFilesMap(Box<dyn std::error::Error>),
 
     /// The request's multipart data was invalid.
     #[error("Invalid multipart data")]
diff --git a/src/http/multipart.rs b/src/http/multipart.rs
index 5976fe50..c6f5e793 100644
--- a/src/http/multipart.rs
+++ b/src/http/multipart.rs
@@ -77,7 +77,7 @@ pub(super) async fn receive_batch_multipart(
                 let map_str = field.text().await?;
                 map = Some(
                     serde_json::from_str::<HashMap<String, Vec<String>>>(&map_str)
-                        .map_err(ParseRequestError::InvalidFilesMap)?,
+                        .map_err(|e| ParseRequestError::InvalidFilesMap(Box::new(e)))?,
                 );
             }
             _ => {