diff --git a/RecoVertex/KalmanVertexFit/interface/SimpleVertexTree.h b/RecoVertex/KalmanVertexFit/interface/SimpleVertexTree.h
index 7947ed202d12c..792a68423c350 100644
--- a/RecoVertex/KalmanVertexFit/interface/SimpleVertexTree.h
+++ b/RecoVertex/KalmanVertexFit/interface/SimpleVertexTree.h
@@ -106,7 +106,6 @@ class SimpleVertexTree {
   int maxTrack;
   TString* parameterNames[5];
   TrackAssociatorByChi2 * associatorForParamAtPca;
-  std::atomic<int> nFill{0};
 };
 #endif
 
diff --git a/RecoVertex/KalmanVertexFit/src/SimpleVertexTree.cc b/RecoVertex/KalmanVertexFit/src/SimpleVertexTree.cc
index 0ec3891bf5dbe..c3eceb53954c8 100644
--- a/RecoVertex/KalmanVertexFit/src/SimpleVertexTree.cc
+++ b/RecoVertex/KalmanVertexFit/src/SimpleVertexTree.cc
@@ -167,7 +167,7 @@ void SimpleVertexTree::fill(const TrackingVertex * simv)
 void SimpleVertexTree::fill() 
 {
   ++numberOfVertices;
-
+  static std::atomic<int> nFill{0};
   TDirectory* rootDir = gDirectory;
   //
   // fill entry