diff --git a/MuonSpectrometer/MuonIdHelpers/MuonIdHelpers/MmIdHelper.h b/MuonSpectrometer/MuonIdHelpers/MuonIdHelpers/MmIdHelper.h
index ef5ed5e4f3be130ec91fbe4dd3e923d7bf1339e7..56b7837ddc91291cdb796e85f1c7a41208abf895 100644
--- a/MuonSpectrometer/MuonIdHelpers/MuonIdHelpers/MmIdHelper.h
+++ b/MuonSpectrometer/MuonIdHelpers/MuonIdHelpers/MmIdHelper.h
@@ -93,7 +93,8 @@ class MmIdHelper : public MuonIdHelper {
   int gasGap(const Identifier& id) const;
   int multilayer(const Identifier& id) const;
   int channel(const Identifier& id) const;
-  bool measuresPhi(const Identifier& id) const; //Returns true for stereo layers
+  bool isStereo(const Identifier& id) const;
+  bool measuresPhi(const Identifier& id) const; //Returns false
 
   int numberOfMultilayers(const Identifier& id) const;
 
@@ -302,12 +303,16 @@ inline int MmIdHelper::gasGapMin() const {
   return GasGapMin;
 }
 /*******************************************************************************/ 
-inline bool MmIdHelper::measuresPhi(const Identifier& id) const{
-  bool measPhi = false;
+inline bool MmIdHelper::isStereo(const Identifier& id) const{
+  bool isStereo = false;
   int ml = multilayer(id);
   int gg = gasGap(id);
-  if ( (ml==1 && gg>2) || (ml==2 && gg<3) ) measPhi = true;
-  return measPhi;                                                                                               
+  if ( (ml==1 && gg>2) || (ml==2 && gg<3) ) isStereo = true;
+  return isStereo;                                                                                               
+}
+/*******************************************************************************/ 
+inline bool MmIdHelper::measuresPhi(const Identifier& /*id*/) const{
+  return false; 
 }
 /*******************************************************************************/ 
 inline int MmIdHelper::gasGapMax() const {
diff --git a/MuonSpectrometer/MuonReconstruction/MuonDataPrep/MMClusterization/src/SimpleMMClusterBuilderTool.cxx b/MuonSpectrometer/MuonReconstruction/MuonDataPrep/MMClusterization/src/SimpleMMClusterBuilderTool.cxx
index 13e84b367a21dcff1e4147fcb78824977c36d64c..71c65ce170b7b3ad35ca66f3024e2c455d37b214 100644
--- a/MuonSpectrometer/MuonReconstruction/MuonDataPrep/MMClusterization/src/SimpleMMClusterBuilderTool.cxx
+++ b/MuonSpectrometer/MuonReconstruction/MuonDataPrep/MMClusterization/src/SimpleMMClusterBuilderTool.cxx
@@ -17,7 +17,7 @@ Muon::SimpleMMClusterBuilderTool::SimpleMMClusterBuilderTool(const std::string&
   m_mmIdHelper(nullptr)
 {
   declareInterface<IMMClusterBuilderTool>(this);
-  declareProperty("useErrorParametrization",m_useErrorParametrization=false);
+  declareProperty("useErrorParametrization",m_useErrorParametrization=true);
 
 }
 
@@ -197,6 +197,9 @@ StatusCode Muon::SimpleMMClusterBuilderTool::getClusters(std::vector<Muon::MMPre
       if(nmerge<=1) (*covN)(0,0) = covX;
     } else {
       double localUncertainty = 0.074+0.66*theta-0.15*theta*theta;
+      if ( m_mmIdHelper->isStereo(MMprds[i].identify()) ) {
+	localUncertainty = 10.;
+      }
       (*covN)(0,0) = localUncertainty * localUncertainty;
     }
     ATH_MSG_VERBOSE(" make merged prepData at strip " << m_mmIdHelper->channel(MMprds[j].identify()) << " nmerge " << nmerge << " sqrt covX " << sqrt((*covN)(0,0)));