diff --git a/MuonSpectrometer/MuonReconstruction/MuonPatternFinders/MuonPatternFinderTools/MuonHoughPatternTools/src/MuonLayerHoughTool.cxx b/MuonSpectrometer/MuonReconstruction/MuonPatternFinders/MuonPatternFinderTools/MuonHoughPatternTools/src/MuonLayerHoughTool.cxx
index 54e7219730c2b515169174f3b55044e093895030..8c99a27f0a2e3e9e5cbc9883ba7272eba57c37f6 100644
--- a/MuonSpectrometer/MuonReconstruction/MuonPatternFinders/MuonPatternFinderTools/MuonHoughPatternTools/src/MuonLayerHoughTool.cxx
+++ b/MuonSpectrometer/MuonReconstruction/MuonPatternFinders/MuonPatternFinderTools/MuonHoughPatternTools/src/MuonLayerHoughTool.cxx
@@ -42,8 +42,8 @@ namespace Muon {
     ATH_CHECK( detStore()->retrieve( m_detMgr ) );
 
     if( m_doNtuple ){
-      if (Gaudi::Concurrency::ConcurrencyFlags::concurrent()) {
-        // Disabled under concurrency due to thread-safety concerns, but we want to keep it as a debug tool
+      if (Gaudi::Concurrency::ConcurrencyFlags::concurrent() && Gaudi::Concurrency::ConcurrencyFlags::numThreads()>1) {
+        // Disabled for >1 threads due to thread-safety concerns, but we want to keep it as a debug tool
         ATH_MSG_DEBUG("HitNtuple disabled because of concurrency");
 	m_file = 0;
 	m_tree = 0;
diff --git a/Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCombinedTool.cxx b/Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCombinedTool.cxx
index 7f014a60980d5dc67ed9a076d2a4b3bafd753dda..01a400b59841aa44168857cb69b194f4b1b26f55 100644
--- a/Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCombinedTool.cxx
+++ b/Reconstruction/MuonIdentification/MuonCombinedBaseTools/src/MuonCombinedTool.cxx
@@ -12,7 +12,6 @@
 //  (c) ATLAS Combined Muon software
 //////////////////////////////////////////////////////////////////////////////
 
-//<<<<<< INCLUDES                                                       >>>>>>
 #include "MuonRecHelperTools/MuonEDMPrinterTool.h"
 #include "GaudiKernel/ConcurrencyFlags.h"
 #include "MuonCombinedToolInterfaces/IMuonCombinedTagTool.h"
@@ -21,8 +20,6 @@
 #include "MuonCombinedTool.h"
 
 namespace MuonCombined {
- 
-  //<<<<<< CLASS STRUCTURE INITIALIZATION                                 >>>>>>
 
   MuonCombinedTool::MuonCombinedTool (const std::string& type, const std::string& name, const IInterface* parent)
     :	AthAlgTool(type, name, parent),
@@ -48,10 +45,12 @@ namespace MuonCombined {
     ATH_CHECK(m_printer.retrieve());
     ATH_CHECK(m_muonCombinedTagTools.retrieve());
 
-    // debug tree, only in serial mode
-    if(m_runMuonCombinedDebugger && !Gaudi::Concurrency::ConcurrencyFlags::concurrent()) {
-      ATH_CHECK(m_muonCombDebugger.retrieve());
-      m_muonCombDebugger->bookBranches();
+    // debug tree, only for running with 1 thread
+    if(m_runMuonCombinedDebugger) {
+      if (!Gaudi::Concurrency::ConcurrencyFlags::concurrent() || Gaudi::Concurrency::ConcurrencyFlags::numThreads()==1) {
+        ATH_CHECK(m_muonCombDebugger.retrieve());
+        m_muonCombDebugger->bookBranches();
+      }
     }
 
     return StatusCode::SUCCESS;