diff --git a/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.cxx b/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.cxx
index 21dcf4381551add9a0104125a2a4ed57046359da..bd1411f6b6954efe21c3cdea72bb074fdf6e4862 100644
--- a/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.cxx
+++ b/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.cxx
@@ -20,6 +20,7 @@ Muon::SimpleSTgcClusterBuilderTool::SimpleSTgcClusterBuilderTool(const std::stri
 {
   declareProperty("ChargeCut", m_chargeCut=0.0);
   declareProperty("maxHoleSize",m_maxHoleSize=1);
+  declareProperty("addError",m_addError=0);
 }
 
 Muon::SimpleSTgcClusterBuilderTool::~SimpleSTgcClusterBuilderTool()
@@ -151,8 +152,7 @@ StatusCode Muon::SimpleSTgcClusterBuilderTool::getClusters(std::vector<Muon::sTg
         sigmaSq = sigmaSq/(totalCharge*totalCharge*12);
         ATH_MSG_DEBUG("Uncertainty on cluster position is: " << sqrt(sigmaSq));         
         Amg::MatrixX* covN = new Amg::MatrixX(1,1);
-        (*covN)(0,0) = sigmaSq;
-
+        (*covN)(0,0) = sigmaSq + m_addError*m_addError;
         //
         // memory allocated dynamically for the PrepRawData is managed by Event Store in the converters
         //
diff --git a/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.h b/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.h
index 1f1e266eb915d3600061d6301c0a93444d0651a2..f9241c3c8cebfda5a1c809737e35e5d748c6914a 100644
--- a/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.h
+++ b/MuonSpectrometer/MuonReconstruction/MuonDataPrep/STgcClusterization/src/SimpleSTgcClusterBuilderTool.h
@@ -50,6 +50,7 @@ namespace Muon
 
     double m_chargeCut;
     unsigned int m_maxHoleSize;
+    double m_addError;
 
     /// Muon detector manager and helper
     const MuonGM::MuonDetectorManager* m_muonMgr;