diff --git a/typo3/sysext/form/Configuration/Yaml/FormEngineSetup.yaml b/typo3/sysext/form/Configuration/Yaml/FormEngineSetup.yaml
index e0ed2d6d67b504b447678cff85c3dce2b25f835e..89221a18b8dd2ba875bcc574085d3e2e00831d86 100644
--- a/typo3/sysext/form/Configuration/Yaml/FormEngineSetup.yaml
+++ b/typo3/sysext/form/Configuration/Yaml/FormEngineSetup.yaml
@@ -83,6 +83,7 @@ TYPO3:
               label: 'tt_content.finishersDefinition.EmailToSender.subject.label'
               config:
                 type: 'input'
+                eval: 'required'
             recipientAddress:
               label: 'tt_content.finishersDefinition.EmailToSender.recipientAddress.label'
               config: