diff --git a/lib/private/DB/QueryBuilder/ExpressionBuilder/ExpressionBuilder.php b/lib/private/DB/QueryBuilder/ExpressionBuilder/ExpressionBuilder.php
index 59d619b533f84..465e03cada841 100644
--- a/lib/private/DB/QueryBuilder/ExpressionBuilder/ExpressionBuilder.php
+++ b/lib/private/DB/QueryBuilder/ExpressionBuilder/ExpressionBuilder.php
@@ -427,11 +427,11 @@ public function literal($input, $type = null): ILiteral {
 	 *
 	 * @param string $column
 	 * @param mixed $type One of IQueryBuilder::PARAM_*
-	 * @return string
+	 * @return IQueryFunction
 	 */
-	public function castColumn(string $column, $type): string {
-		return (string)(new QueryFunction(
+	public function castColumn(string $column, $type): IQueryFunction {
+		return new QueryFunction(
 			$this->helper->quoteColumnName($column)
-		));
+		);
 	}
 }
diff --git a/lib/private/DB/QueryBuilder/ExpressionBuilder/OCIExpressionBuilder.php b/lib/private/DB/QueryBuilder/ExpressionBuilder/OCIExpressionBuilder.php
index 6a700dffb1228..5d315de37b467 100644
--- a/lib/private/DB/QueryBuilder/ExpressionBuilder/OCIExpressionBuilder.php
+++ b/lib/private/DB/QueryBuilder/ExpressionBuilder/OCIExpressionBuilder.php
@@ -163,16 +163,16 @@ public function nonEmptyString(string $x): string {
 	 *
 	 * @param string $column
 	 * @param mixed $type One of IQueryBuilder::PARAM_*
-	 * @return string
+	 * @return IQueryFunction
 	 */
-	public function castColumn(string $column, $type): string {
+	public function castColumn(string $column, $type): IQueryFunction {
 		if ($type === IQueryBuilder::PARAM_STR) {
 			$column = $this->helper->quoteColumnName($column);
-			return (string)(new QueryFunction('to_char(' . $column . ')'));
+			return new QueryFunction('to_char(' . $column . ')');
 		}
 		if ($type === IQueryBuilder::PARAM_INT) {
 			$column = $this->helper->quoteColumnName($column);
-			return (string)(new QueryFunction('to_number(to_char(' . $column . '))'));
+			return new QueryFunction('to_number(to_char(' . $column . '))');
 		}
 
 		return parent::castColumn($column, $type);
diff --git a/lib/private/DB/QueryBuilder/ExpressionBuilder/PgSqlExpressionBuilder.php b/lib/private/DB/QueryBuilder/ExpressionBuilder/PgSqlExpressionBuilder.php
index b03cbf7ef0f7a..3e8cdd698b488 100644
--- a/lib/private/DB/QueryBuilder/ExpressionBuilder/PgSqlExpressionBuilder.php
+++ b/lib/private/DB/QueryBuilder/ExpressionBuilder/PgSqlExpressionBuilder.php
@@ -26,6 +26,7 @@
 
 use OC\DB\QueryBuilder\QueryFunction;
 use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\DB\QueryBuilder\IQueryFunction;
 
 class PgSqlExpressionBuilder extends ExpressionBuilder {
 
@@ -34,14 +35,14 @@ class PgSqlExpressionBuilder extends ExpressionBuilder {
 	 *
 	 * @param string $column
 	 * @param mixed $type One of IQueryBuilder::PARAM_*
-	 * @return string
+	 * @return IQueryFunction
 	 */
-	public function castColumn($column, $type): string {
+	public function castColumn($column, $type): IQueryFunction {
 		switch ($type) {
 			case IQueryBuilder::PARAM_INT:
-				return (string)(new QueryFunction('CAST(' . $this->helper->quoteColumnName($column) . ' AS INT)'));
+				return new QueryFunction('CAST(' . $this->helper->quoteColumnName($column) . ' AS INT)');
 			case IQueryBuilder::PARAM_STR:
-				return (string)(new QueryFunction('CAST(' . $this->helper->quoteColumnName($column) . ' AS TEXT)'));
+				return new QueryFunction('CAST(' . $this->helper->quoteColumnName($column) . ' AS TEXT)');
 			default:
 				return parent::castColumn($column, $type);
 		}
diff --git a/lib/public/DB/QueryBuilder/IExpressionBuilder.php b/lib/public/DB/QueryBuilder/IExpressionBuilder.php
index 29439aac7d300..23e98f56a541e 100644
--- a/lib/public/DB/QueryBuilder/IExpressionBuilder.php
+++ b/lib/public/DB/QueryBuilder/IExpressionBuilder.php
@@ -434,11 +434,11 @@ public function literal($input, $type = null): ILiteral;
 	 *
 	 * @param string $column
 	 * @param mixed $type One of IQueryBuilder::PARAM_*
-	 * @return string
+	 * @return IQueryFunction
 	 * @since 9.0.0
 	 *
 	 * @psalm-taint-sink sql $column
 	 * @psalm-taint-sink sql $type
 	 */
-	public function castColumn(string $column, $type): string;
+	public function castColumn(string $column, $type): IQueryFunction;
 }