diff --git a/app/Rules/IsValidActionExpression.php b/app/Rules/IsValidActionExpression.php
index f1c488331d..ae22e48708 100644
--- a/app/Rules/IsValidActionExpression.php
+++ b/app/Rules/IsValidActionExpression.php
@@ -21,6 +21,8 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+declare(strict_types=1);
+
 namespace FireflyIII\Rules;
 
 use Closure;
diff --git a/app/TransactionRules/Expressions/ActionExpression.php b/app/TransactionRules/Expressions/ActionExpression.php
index c4069dee92..59b9770e14 100644
--- a/app/TransactionRules/Expressions/ActionExpression.php
+++ b/app/TransactionRules/Expressions/ActionExpression.php
@@ -133,7 +133,7 @@ class ActionExpression
         return $this->validationError === null;
     }
 
-    public function getValidationError()
+    public function getValidationError(): ?SyntaxError
     {
         return $this->validationError;
     }
diff --git a/app/TransactionRules/Expressions/ActionExpressionLanguageProvider.php b/app/TransactionRules/Expressions/ActionExpressionLanguageProvider.php
index fbb3df1725..2c54752b00 100644
--- a/app/TransactionRules/Expressions/ActionExpressionLanguageProvider.php
+++ b/app/TransactionRules/Expressions/ActionExpressionLanguageProvider.php
@@ -20,6 +20,8 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+declare(strict_types=1);
+
 namespace FireflyIII\TransactionRules\Expressions;
 
 use Symfony\Component\ExpressionLanguage\ExpressionFunction;