diff --git a/entity/Letter_entity/Letter_entity.aod b/entity/Letter_entity/Letter_entity.aod
index ac26bb0328f2c190da97535ced5c58beb728b6fe..4db05f0d1dfd30aca20527a0f508251ae52bce75 100644
--- a/entity/Letter_entity/Letter_entity.aod
+++ b/entity/Letter_entity/Letter_entity.aod
@@ -2,6 +2,7 @@
 <entity xmlns="http://www.adito.de/2018/ao/Model" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" VERSION="1.3.11" xsi:schemaLocation="http://www.adito.de/2018/ao/Model adito://models/xsd/entity/1.3.11">
   <name>Letter_entity</name>
   <majorModelMode>DISTRIBUTED</majorModelMode>
+  <onValidation>%aditoprj%/entity/Letter_entity/onValidation.js</onValidation>
   <recordContainer>jdito</recordContainer>
   <entityFields>
     <entityProvider>
diff --git a/entity/Letter_entity/onValidation.js b/entity/Letter_entity/onValidation.js
new file mode 100644
index 0000000000000000000000000000000000000000..083fd4dbe6888e3bd8696dea5f480a2a5dfd34b7
--- /dev/null
+++ b/entity/Letter_entity/onValidation.js
@@ -0,0 +1,8 @@
+import("system.vars");
+import("system.translate");
+import("system.result");
+
+if (!vars.get("$field.bindata") && !vars.get("$field.DOCUMENT_TEMPLATE"))
+{
+    result.string(translate.text("Please select a documenttemplate or upload a new file."))
+}
\ No newline at end of file