diff --git a/include/SHiP/EventHeader.hpp b/include/SHiP/EventHeader.hpp
index d0aacf7..5f9f38d 100644
--- a/include/SHiP/EventHeader.hpp
+++ b/include/SHiP/EventHeader.hpp
@@ -8,12 +8,12 @@ namespace SHiP {
 struct EventHeader {
   double weight{1.0};  ///< Event weight (e.g. P_DIS / nReplicas)
   std::int64_t original_event_id{
-      -1};                          ///< Originating event id, e.g. the muon
-                                    ///< event that seeded this replica
-                                    ///< (-1 = none). Event-level provenance,
-                                    ///< distinct from MCParticle::mother_id,
-                                    ///< which links particles within an event.
-  std::int64_t aegir_event_id{-1};  // What is the ID of this event from aegir
+      -1};  ///< Originating event id, e.g. the muon
+            ///< event that seeded this replica
+            ///< (-1 = none). Event-level provenance,
+            ///< distinct from MCParticle::mother_id,
+            ///< which links particles within an event.
+
   bool operator==(EventHeader const&) const = default;
 };
 
diff --git a/include/SHiP/LinkDef.h b/include/SHiP/LinkDef.h
index 0a70e60..8ef88fa 100644
--- a/include/SHiP/LinkDef.h
+++ b/include/SHiP/LinkDef.h
@@ -55,7 +55,7 @@
 #pragma link off all functions;
 
 // Event metadata
-#pragma link C++ options=version(3) class SHiP::EventHeader+;
+#pragma link C++ options=version(2) class SHiP::EventHeader+;
 
 // MC / generation
 #pragma link C++ options=version(4) class SHiP::MCParticle+;
diff --git a/tests/data/reference_head.root b/tests/data/reference_head.root
index de9e6cb..33a77b8 100644
Binary files a/tests/data/reference_head.root and b/tests/data/reference_head.root differ
diff --git a/tests/data/schema_snapshot.txt b/tests/data/schema_snapshot.txt
index a2b9b13..eee52c8 100644
--- a/tests/data/schema_snapshot.txt
+++ b/tests/data/schema_snapshot.txt
@@ -1,8 +1,7 @@
 # TClass layout (version, checksum, data members)
-class SHiP::EventHeader version=3 checksum=0xa95503fd
+class SHiP::EventHeader version=2 checksum=0xd65dd49a
   double weight
   long original_event_id
-  long aegir_event_id
 class SHiP::MCParticle version=4 checksum=0x8d1ef3c
   int pdg_code
   array<double,3> vertex
@@ -83,10 +82,9 @@ class SHiP::RecParticle version=3 checksum=0xc908f3a0
   int creator_process
   double ip_pv
 # RNTuple field tree (one top-level field per dictionary class)
-SHiP__EventHeader : SHiP::EventHeader (typever=3, checksum=0xa95503fd)
+SHiP__EventHeader : SHiP::EventHeader (typever=2, checksum=0xd65dd49a)
   weight : double (typever=0)
   original_event_id : std::int64_t (typever=0)
-  aegir_event_id : std::int64_t (typever=0)
 SHiP__MCParticle : SHiP::MCParticle (typever=4, checksum=0x8d1ef3c)
   pdg_code : std::int32_t (typever=0)
   vertex : std::array<double,3> (typever=0)