diff --git a/src/db/mod.rs b/src/db/mod.rs
index 723df9e..6364a6c 100644
--- a/src/db/mod.rs
+++ b/src/db/mod.rs
@@ -57,12 +57,12 @@ impl From<SqliteError> for PixivDownloaderDbError {
 }
 
 #[cfg(all(feature = "db_sqlite", feature = "server"))]
-pub trait Optional2Extension<T> {
-    fn optional2(self) -> Result<Option<T>, PixivDownloaderDbError>;
+pub trait Optional2Extension<T, E> {
+    fn optional2(self) -> Result<Option<T>, E>;
 }
 
 #[cfg(all(feature = "db_sqlite", feature = "server"))]
-impl<T> Optional2Extension<T> for Result<T, PixivDownloaderDbError> {
+impl<T> Optional2Extension<T, PixivDownloaderDbError> for Result<T, PixivDownloaderDbError> {
     fn optional2(self) -> Result<Option<T>, PixivDownloaderDbError> {
         match self {
             Ok(v) => Ok(Some(v)),
@@ -80,6 +80,22 @@ impl<T> Optional2Extension<T> for Result<T, PixivDownloaderDbError> {
     }
 }
 
+#[cfg(all(feature = "db_sqlite", feature = "server"))]
+impl<T> Optional2Extension<T, SqliteError> for Result<T, SqliteError> {
+    fn optional2(self) -> Result<Option<T>, SqliteError> {
+        match self {
+            Ok(v) => Ok(Some(v)),
+            Err(e) => match e {
+                SqliteError::DbError(e) => match e {
+                    rusqlite::Error::QueryReturnedNoRows => Ok(None),
+                    _ => Err(SqliteError::DbError(e)),
+                },
+                _ => Err(e),
+            },
+        }
+    }
+}
+
 #[cfg(not(feature = "db_sqlite"))]
 compile_error!("No database backend is enabled.");
 
diff --git a/src/db/sqlite/db.rs b/src/db/sqlite/db.rs
index 967f5d7..259f178 100644
--- a/src/db/sqlite/db.rs
+++ b/src/db/sqlite/db.rs
@@ -383,9 +383,9 @@ impl PixivDownloaderSqlite {
     }
 
     #[cfg(feature = "server")]
-    async fn get_push_task(&self, id: u64) -> Result<Option<PushTask>, PixivDownloaderDbError> {
+    async fn get_push_task(&self, id: u64) -> Result<Option<PushTask>, SqliteError> {
         let con = self.db.lock().await;
-        con.query_row_and_then::<PushTask, PixivDownloaderDbError, _, _>(
+        con.query_row_and_then::<PushTask, SqliteError, _, _>(
             "SELECT * FROM push_task WHERE id = ?;",
             [id],
             |row| {
diff --git a/src/db/sqlite/error.rs b/src/db/sqlite/error.rs
index ef0ca2a..b62753f 100644
--- a/src/db/sqlite/error.rs
+++ b/src/db/sqlite/error.rs
@@ -3,4 +3,5 @@ pub enum SqliteError {
     DbError(rusqlite::Error),
     DatabaseVersionTooNew,
     UserNameAlreadyExists,
+    SerdeError(serde_json::Error),
 }
diff --git a/src/server/push/index.rs b/src/server/push/index.rs
index 5436441..d731e55 100644
--- a/src/server/push/index.rs
+++ b/src/server/push/index.rs
@@ -105,7 +105,8 @@ impl PushContext {
                         .db
                         .get_push_task(id)
                         .await
-                        .try_err3(500, "Failed to get push task:")?;
+                        .try_err3(500, "Failed to get push task:")?
+                        .try_err3(404, "Push task not found.")?;
                     Ok(serde_json::to_value(re).try_err3(500, "Failed to serialize result:")?)
                 }
             },