diff --git a/programs/Hadrons/AWilson.cc b/programs/Hadrons/AWilson.cc
index 2f8483f3..f9de0926 100644
--- a/programs/Hadrons/AWilson.cc
+++ b/programs/Hadrons/AWilson.cc
@@ -29,6 +29,7 @@ directory.
 #include <Hadrons/Environment.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
diff --git a/programs/Hadrons/Application.cc b/programs/Hadrons/Application.cc
index 5cdb6ed2..1a24f8b6 100644
--- a/programs/Hadrons/Application.cc
+++ b/programs/Hadrons/Application.cc
@@ -29,6 +29,7 @@ directory.
 #include <Hadrons/Graph.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
diff --git a/programs/Hadrons/CMeson.cc b/programs/Hadrons/CMeson.cc
index c171fb95..a6e958f9 100644
--- a/programs/Hadrons/CMeson.cc
+++ b/programs/Hadrons/CMeson.cc
@@ -28,6 +28,7 @@ directory.
 #include <Hadrons/CMeson.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
@@ -85,7 +86,7 @@ void CMeson::execute(Environment &env)
         result.corr[iSink].resize(Ns*Ns);
         for (unsigned int iSrc = 0; iSrc < Ns*Ns; ++iSrc)
         {
-            c    = trace(g[iSink]*q1*g[iSrc]*g5*adj(q2)*g5);
+            c = trace(g[iSink]*q1*g[iSrc]*g5*adj(q2)*g5);
             sliceSum(c, buf, Tp);
             result.corr[iSink][iSrc].resize(buf.size());
             for (unsigned int t = 0; t < buf.size(); ++t)
diff --git a/programs/Hadrons/Factory.hpp b/programs/Hadrons/Factory.hpp
index 2b219dcc..e609949a 100644
--- a/programs/Hadrons/Factory.hpp
+++ b/programs/Hadrons/Factory.hpp
@@ -47,7 +47,7 @@ public:
     virtual ~Factory(void) = default;
     // registration
     void registerBuilder(const std::string type, const Func &f);
-    // get module list
+    // get builder list
     std::vector<std::string> getBuilderList(void) const;
     // factory
     std::unique_ptr<T> create(const std::string type,
@@ -91,7 +91,7 @@ std::unique_ptr<T> Factory<T>::create(const std::string type,
     {
         func = builder_.at(type);
     }
-    catch (std::out_of_range)
+    catch (std::out_of_range &)
     {
         HADRON_ERROR("object of type '" + type + "' unknown");
     }
diff --git a/programs/Hadrons/FermionAction.cc b/programs/Hadrons/FermionAction.cc
index 0857008b..fdd9530c 100644
--- a/programs/Hadrons/FermionAction.cc
+++ b/programs/Hadrons/FermionAction.cc
@@ -28,6 +28,7 @@ directory.
 #include <Hadrons/FermionAction.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
diff --git a/programs/Hadrons/Global.cc b/programs/Hadrons/Global.cc
index 18c3028e..6b855cda 100644
--- a/programs/Hadrons/Global.cc
+++ b/programs/Hadrons/Global.cc
@@ -28,6 +28,7 @@ directory.
 #include <Hadrons/Global.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 HadronsLogger Hadrons::HadronsLogError(1,"Error");
diff --git a/programs/Hadrons/Global.hpp b/programs/Hadrons/Global.hpp
index 39758b7e..f5a5c144 100644
--- a/programs/Hadrons/Global.hpp
+++ b/programs/Hadrons/Global.hpp
@@ -28,15 +28,20 @@ directory.
 #ifndef Hadrons_Global_hpp_
 #define Hadrons_Global_hpp_
 
-#include <Grid.h>
 #include <set>
 #include <stack>
+#include <Grid.h>
 
 #define BEGIN_HADRONS_NAMESPACE \
+namespace Grid {\
+using namespace QCD;\
 namespace Hadrons {\
-using namespace Grid;\
-using namespace QCD;
-#define END_HADRONS_NAMESPACE }
+using Grid::operator<<;
+#define END_HADRONS_NAMESPACE }}
+
+/* the 'using Grid::operator<<;' statement prevents a very nasty compilation
+ * error with GCC (clang compiles fine without it).
+ */
 
 BEGIN_HADRONS_NAMESPACE
 
diff --git a/programs/Hadrons/Graph.hpp b/programs/Hadrons/Graph.hpp
index 8b8afcc6..c7591350 100644
--- a/programs/Hadrons/Graph.hpp
+++ b/programs/Hadrons/Graph.hpp
@@ -105,8 +105,8 @@ private:
     void depthFirstSearch(void);
     void depthFirstSearch(const T &root);
 private:
-    std::map<T, bool>              isMarked_;
-    std::set<Edge>                 edgeSet_;
+    std::map<T, bool> isMarked_;
+    std::set<Edge>    edgeSet_;
 };
 
 // build depedency matrix from topological sorts
diff --git a/programs/Hadrons/Hadrons.cc b/programs/Hadrons/Hadrons.cc
index 73ac03f9..da5e02b1 100644
--- a/programs/Hadrons/Hadrons.cc
+++ b/programs/Hadrons/Hadrons.cc
@@ -27,6 +27,8 @@ directory.
 
 #include <Hadrons/Application.hpp>
 
+using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 int main(int argc, char *argv[])
diff --git a/programs/Hadrons/MQuark.cc b/programs/Hadrons/MQuark.cc
index 575914e4..04f9042d 100644
--- a/programs/Hadrons/MQuark.cc
+++ b/programs/Hadrons/MQuark.cc
@@ -28,6 +28,7 @@ directory.
 #include <Hadrons/MQuark.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
diff --git a/programs/Hadrons/MSource.cc b/programs/Hadrons/MSource.cc
index f09c0b1d..3897db7c 100644
--- a/programs/Hadrons/MSource.cc
+++ b/programs/Hadrons/MSource.cc
@@ -28,7 +28,9 @@ directory.
 #include <Hadrons/MSource.hpp>
 
 #define ERROR_SUF " (source '" << getName() << "')"
+
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
diff --git a/programs/Hadrons/Module.cc b/programs/Hadrons/Module.cc
index 1437046e..a590b81a 100644
--- a/programs/Hadrons/Module.cc
+++ b/programs/Hadrons/Module.cc
@@ -28,6 +28,7 @@ directory.
 #include <Hadrons/Module.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************
diff --git a/programs/Hadrons/SRBPrecCG.cc b/programs/Hadrons/SRBPrecCG.cc
index 22206ed3..ff4a50d5 100644
--- a/programs/Hadrons/SRBPrecCG.cc
+++ b/programs/Hadrons/SRBPrecCG.cc
@@ -28,6 +28,7 @@ directory.
 #include <Hadrons/SRBPrecCG.hpp>
 
 using namespace Grid;
+using namespace QCD;
 using namespace Hadrons;
 
 /******************************************************************************