diff --git a/include/edm4hep/Constants.h b/include/edm4hep/Constants.h
index 6857a56f2..7734cdd8a 100644
--- a/include/edm4hep/Constants.h
+++ b/include/edm4hep/Constants.h
@@ -21,6 +21,7 @@
 
 namespace edm4hep {
 static constexpr const char* CellIDEncoding = "CellIDEncoding";
-}
+static constexpr const char* EventHeader = "EventHeader";
+} // namespace edm4hep
 
 #endif // EDM4HEP_CONSTANTS_H