diff --git a/src/doc/specification/Specification-of-the-Entity-API.md b/src/doc/specification/Specification-of-the-Entity-API.md
index 93b39f5333b9f80c9f4485fc00c2f827ad60792a..5ef05b7898d40e43f320c9e3519a6d9520efffcd 100644
--- a/src/doc/specification/Specification-of-the-Entity-API.md
+++ b/src/doc/specification/Specification-of-the-Entity-API.md
@@ -1,4 +1,7 @@
 # Specification of the Entity API
+
+**Warning:** This specification is outdated. It is included to serve as a starting point for a more up-to-date description of the entity API.
+
 Version: 0.1.0r1
 
 Author: Timm Fitschen