diff --git a/SimTracker/TrackAssociation/interface/trackHitsToClusterRefs.h b/SimTracker/TrackAssociation/interface/trackHitsToClusterRefs.h
index 171a7eb6f2efe..89b2ed5733bc0 100644
--- a/SimTracker/TrackAssociation/interface/trackHitsToClusterRefs.h
+++ b/SimTracker/TrackAssociation/interface/trackHitsToClusterRefs.h
@@ -13,9 +13,9 @@
 #include "FWCore/MessageLogger/interface/MessageLogger.h"
 
 namespace track_associator {
-  const TrackingRecHit *getHitFromIter(trackingRecHit_iterator iter) { return &(**iter); }
+  inline const TrackingRecHit *getHitFromIter(trackingRecHit_iterator iter) { return &(**iter); }
 
-  const TrackingRecHit *getHitFromIter(TrackingRecHitCollection::const_iterator iter) { return &(*iter); }
+  inline const TrackingRecHit *getHitFromIter(TrackingRecHitCollection::const_iterator iter) { return &(*iter); }
 
   template <typename iter>
   std::vector<OmniClusterRef> hitsToClusterRefs(iter begin, iter end) {
diff --git a/SimTracker/TrackerMaterialAnalysis/plugins/ListGroupsMaterialDifference.h b/SimTracker/TrackerMaterialAnalysis/plugins/ListGroupsMaterialDifference.h
index a775a8629c04f..5daa93969b5d4 100644
--- a/SimTracker/TrackerMaterialAnalysis/plugins/ListGroupsMaterialDifference.h
+++ b/SimTracker/TrackerMaterialAnalysis/plugins/ListGroupsMaterialDifference.h
@@ -3,6 +3,6 @@
 #ifndef SIMTRACKER_TRACKERMATERIALANALYSIS_LISTGROUPS_MATERIALDIFFERENCE_H
 #define SIMTRACKER_TRACKERMATERIALANALYSIS_LISTGROUPS_MATERIALDIFFERENCE_H
 
-void ListGroups::fillMaterialDifferences() {}
+inline void ListGroups::fillMaterialDifferences() {}
 
 #endif  //  SIMTRACKER_TRACKERMATERIALANALYSIS_LISTGROUPS_MATERIALDIFFERENCE_H
diff --git a/SimTracker/TrackerMaterialAnalysis/plugins/dd4hep/DD4hep_ListGroupsMaterialDifference.h b/SimTracker/TrackerMaterialAnalysis/plugins/dd4hep/DD4hep_ListGroupsMaterialDifference.h
index 9a4ec5bd11cbc..20c69de826e8f 100644
--- a/SimTracker/TrackerMaterialAnalysis/plugins/dd4hep/DD4hep_ListGroupsMaterialDifference.h
+++ b/SimTracker/TrackerMaterialAnalysis/plugins/dd4hep/DD4hep_ListGroupsMaterialDifference.h
@@ -3,6 +3,6 @@
 #ifndef DD4HEP_SIMTRACKER_TRACKERMATERIALANALYSIS_LISTGROUPS_MATERIALDIFFERENCE_H
 #define DD4HEP_SIMTRACKER_TRACKERMATERIALANALYSIS_LISTGROUPS_MATERIALDIFFERENCE_H
 
-void DD4hep_ListGroups::fillMaterialDifferences() {}
+inline void DD4hep_ListGroups::fillMaterialDifferences() {}
 
 #endif  //  DD4HEP_SIMTRACKER_TRACKERMATERIALANALYSIS_LISTGROUPS_MATERIALDIFFERENCE_H