diff --git a/plugins/org.etsi.mts.tdl.tx/src/org/etsi/mts/tdl/TDLtx.xtext b/plugins/org.etsi.mts.tdl.tx/src/org/etsi/mts/tdl/TDLtx.xtext
index 928e39eba329ef3dd0590afd85fd8ff2bc5c5132..94528f6a6749db10b5fe115d2b9c63ee82d08392 100644
--- a/plugins/org.etsi.mts.tdl.tx/src/org/etsi/mts/tdl/TDLtx.xtext
+++ b/plugins/org.etsi.mts.tdl.tx/src/org/etsi/mts/tdl/TDLtx.xtext
@@ -179,6 +179,15 @@ SimpleDataInstance returns tdl::SimpleDataInstance:
     name=Identifier 
 ;
 
+EnumDataInstance returns tdl::SimpleDataInstance:
+    AnnotationCommentFragment
+    dataType=[tdl::DataType|Identifier]?
+    //for backwards compatibility -> Predefined Booleans now True and False
+    //(name=Identifier | name=BOOLEANNAME)
+    name=Identifier 
+;
+
+
 StructuredDataType returns tdl::StructuredDataType:
     AnnotationCommentFragment
     'Structure' name=Identifier
@@ -301,7 +310,7 @@ EnumDataType returns tdl::EnumDataType:
     AnnotationCommentFragment
     'Enumerated' name=Identifier
     BEGIN
-        value+=SimpleDataInstance (',' value+=SimpleDataInstance)*
+        value+=EnumDataInstance (',' value+=EnumDataInstance)*
     END
 ;