diff --git a/SimDataFormats/HiGenData/interface/GenHIEvent.h b/SimDataFormats/HiGenData/interface/GenHIEvent.h
index be9ab9ee0ad6f..14c329c28b944 100644
--- a/SimDataFormats/HiGenData/interface/GenHIEvent.h
+++ b/SimDataFormats/HiGenData/interface/GenHIEvent.h
@@ -64,14 +64,14 @@ namespace edm {
       double EtMR() const {return EtMR_;}
       int NchargedPtCut() const {return nChargedPtCut_;}
       int NchargedPtCutMR() const {return nChargedPtCutMR_;}
-      void setGenParticles(const reco::GenParticleCollection*) const;
+      void setGenParticles(const reco::GenParticleCollection*);
       const std::vector<reco::GenParticleRef>    getSubEvent(unsigned int sub_id) const;
 
       int           getNsubs() const {return subevents_.size();}
 
    private:
 
-      mutable SubEventCollection subevents_;
+      SubEventCollection subevents_;
       int sel_;
 
       double b_;
diff --git a/SimDataFormats/HiGenData/src/GenHIEvent.cc b/SimDataFormats/HiGenData/src/GenHIEvent.cc
index 1191e6d191d70..5997ff0214fc2 100644
--- a/SimDataFormats/HiGenData/src/GenHIEvent.cc
+++ b/SimDataFormats/HiGenData/src/GenHIEvent.cc
@@ -2,7 +2,7 @@
 #include "SimDataFormats/HiGenData/interface/GenHIEvent.h"
 using namespace edm;
 
-void GenHIEvent::setGenParticles(const reco::GenParticleCollection* input) const {
+void GenHIEvent::setGenParticles(const reco::GenParticleCollection* input) {
   subevents_.reserve(nhard_);
   for(int i = 0; i < nhard_; ++i){
     std::vector<reco::GenParticleRef> refs;