diff --git a/lib/qcd/action/gauge/GaugeImpl.h b/lib/qcd/action/gauge/GaugeImpl.h
index fd3bf55a..5ef9f107 100644
--- a/lib/qcd/action/gauge/GaugeImpl.h
+++ b/lib/qcd/action/gauge/GaugeImpl.h
@@ -49,8 +49,8 @@ template <class Gimpl> class WilsonLoops;
 #define INHERIT_FIELD_TYPES(Impl) \
   typedef typename Impl::Field Field; 
 
-
-template <class S, int Nrepresentation = Nc > class GaugeImplTypes {
+// hard codes the exponential approximation in the template
+template <class S, int Nrepresentation = Nc, int Nexp = 12 > class GaugeImplTypes {
 public:
   typedef S Simd;
 
@@ -75,6 +75,7 @@ public:
     }
   }
 
+  // HMC auxiliary functions
   static inline void generate_momenta(Field& P, GridParallelRNG& pRNG){
     // specific for SU gauge fields
     LinkField Pmu(P._grid);
@@ -85,15 +86,15 @@ public:
     }
   }
 
-  static inline void update_field(Field& P, Field& U, double ep, unsigned int Nexp){
-
+   
+  
+  static inline void update_field(Field& P, Field& U, double ep){
     for (int mu = 0; mu < Nd; mu++) {
       auto Umu = PeekIndex<LorentzIndex>(U, mu);
       auto Pmu = PeekIndex<LorentzIndex>(P, mu);
       Umu = expMat(Pmu, ep, Nexp) * Umu;
       PokeIndex<LorentzIndex>(U, ProjectOnGroup(Umu), mu);
     }
-
   }
 
   static inline RealD FieldSquareNorm(Field& U){
diff --git a/lib/qcd/hmc/integrators/Integrator.h b/lib/qcd/hmc/integrators/Integrator.h
index d2c1aef1..f5e5a37c 100644
--- a/lib/qcd/hmc/integrators/Integrator.h
+++ b/lib/qcd/hmc/integrators/Integrator.h
@@ -155,7 +155,8 @@ class Integrator {
               << " dt " << ep << " : t_U " << t_U << std::endl;
   }
   void update_U(MomentaField& Mom, Field& U, double ep) {
-    FieldImplementation::update_field(Mom, U, ep, Params.Nexp);
+    // exponential of Mom*U in the gauge fields case
+    FieldImplementation::update_field(Mom, U, ep);
 
     // Update the smeared fields, can be implemented as observer
     Smearer.set_Field(U);