diff --git a/backend/src/error.rs b/backend/src/error.rs
index 689780c..0c272bb 100644
--- a/backend/src/error.rs
+++ b/backend/src/error.rs
@@ -12,6 +12,7 @@ pub type AppResult<T> = Result<T, AppError>;
 pub struct AppError {
     status: StatusCode,
     message: String,
+    code: Option<String>,
 }
 
 impl AppError {
@@ -19,6 +20,7 @@ impl AppError {
         Self {
             status,
             message: message.into(),
+            code: None,
         }
     }
 
@@ -26,6 +28,10 @@ impl AppError {
         Self::new(StatusCode::BAD_REQUEST, message)
     }
 
+    pub fn conflict(message: impl Into<String>) -> Self {
+        Self::new(StatusCode::CONFLICT, message)
+    }
+
     pub fn unauthorized() -> Self {
         Self::new(StatusCode::UNAUTHORIZED, "unauthorized")
     }
@@ -37,6 +43,11 @@ impl AppError {
     pub fn internal<E: Display>(error: E) -> Self {
         Self::new(StatusCode::INTERNAL_SERVER_ERROR, error.to_string())
     }
+
+    pub fn with_code(mut self, code: impl Into<String>) -> Self {
+        self.code = Some(code.into());
+        self
+    }
 }
 
 impl IntoResponse for AppError {
@@ -44,6 +55,7 @@ impl IntoResponse for AppError {
         let status = self.status;
         let body = Json(ErrorResponse {
             error: self.message,
+            code: self.code,
         });
         (status, body).into_response()
     }
@@ -52,6 +64,8 @@ impl IntoResponse for AppError {
 #[derive(Serialize)]
 struct ErrorResponse {
     error: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    code: Option<String>,
 }
 
 impl From<diesel::result::Error> for AppError {
diff --git a/backend/src/routes/documents.rs b/backend/src/routes/documents.rs
index 2ca83cc..5eac634 100644
--- a/backend/src/routes/documents.rs
+++ b/backend/src/routes/documents.rs
@@ -1151,9 +1151,10 @@ pub async fn update_document(
         match update_result.execute(&mut conn) {
             Ok(_) => {}
             Err(diesel::result::Error::DatabaseError(DatabaseErrorKind::UniqueViolation, _)) => {
-                return Err(AppError::bad_request(
+                return Err(AppError::conflict(
                     "another document in this folder already uses that filename",
-                ));
+                )
+                .with_code("duplicate_filename"));
             }
             Err(err) => return Err(AppError::from(err)),
         }
@@ -1822,7 +1823,7 @@ async fn process_upload(
 
     let (document, version) = {
         let mut conn = state.db_for_tenant(tenant_id)?;
-        conn.transaction(|conn| {
+        let transaction_result = conn.transaction(|conn| {
             let new_document = NewDocument {
                 id: doc_id,
                 filename: stored_filename.clone(),
@@ -1859,7 +1860,18 @@ async fn process_upload(
             let version: DocumentVersion = document_versions::table.find(version_id).first(conn)?;
 
             Ok::<_, diesel::result::Error>((document, version))
-        })?
+        });
+
+        match transaction_result {
+            Ok(result) => result,
+            Err(diesel::result::Error::DatabaseError(DatabaseErrorKind::UniqueViolation, _)) => {
+                return Err(AppError::conflict(
+                    "another document in this folder already uses that filename",
+                )
+                .with_code("duplicate_filename"))
+            }
+            Err(err) => return Err(AppError::from(err)),
+        }
     };
 
     let detail = {