diff --git a/orchestration/src/main/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformer.java b/orchestration/src/main/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformer.java
index 4806489ce..193fddedc 100644
--- a/orchestration/src/main/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformer.java
+++ b/orchestration/src/main/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformer.java
@@ -82,6 +82,10 @@ static PromptTemplatingModuleConfigPrompt toTemplateModuleConfig(
      * To be fixed with https://github.tools.sap/AI/llm-orchestration/issues/662
      */
     if (config instanceof TemplateRef) {
+      if (!prompt.getMessages().isEmpty()) {
+        throw new IllegalArgumentException(
+            "Prompt must not contain messages when using a template reference");
+      }
       return config;
     }
 
diff --git a/orchestration/src/test/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformerTest.java b/orchestration/src/test/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformerTest.java
index e01415733..697640570 100644
--- a/orchestration/src/test/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformerTest.java
+++ b/orchestration/src/test/java/com/sap/ai/sdk/orchestration/ConfigToRequestTransformerTest.java
@@ -29,6 +29,17 @@ void testThrowsOnMissingMessages() {
         .hasMessageContaining("A prompt is required");
   }
 
+  @Test
+  void testThrowsOnTemplateRefWithMessages() {
+    var prompt = new OrchestrationPrompt("Foo bar");
+    var templateRef =
+        TemplateConfig.reference().byId("21cb1358-0bf1-4f43-870b-00f14d0f9f16").toLowLevel();
+
+    assertThatThrownBy(() -> ConfigToRequestTransformer.toTemplateModuleConfig(prompt, templateRef))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessageContaining("Prompt must not contain messages when using a template reference");
+  }
+
   @Test
   void testEmptyTemplateConfig() {
     var systemMessage = new SystemMessage("foo");