diff --git a/roofit/roofitcore/inc/RooMinimizer.h b/roofit/roofitcore/inc/RooMinimizer.h
index 6d590a983d547..e614e62dbb296 100644
--- a/roofit/roofitcore/inc/RooMinimizer.h
+++ b/roofit/roofitcore/inc/RooMinimizer.h
@@ -48,7 +48,7 @@ class RooPlot ;
 namespace RooFit {
 namespace TestStatistics {
 class LikelihoodSerial;
-class LikelihoodGradientSerial;
+//class LikelihoodGradientSerial;
 }
 } // namespace RooFit
 
@@ -58,8 +58,8 @@ class RooMinimizer : public TObject {
 
   explicit RooMinimizer(RooAbsReal &function, FcnMode fcnMode = FcnMode::classic);
   static std::unique_ptr<RooMinimizer> create(RooAbsReal &function, FcnMode fcnMode = FcnMode::classic);
-  template <typename LikelihoodWrapperT = RooFit::TestStatistics::LikelihoodSerial,
-            typename LikelihoodGradientWrapperT = RooFit::TestStatistics::LikelihoodGradientSerial>
+  template <typename LikelihoodWrapperT /*= RooFit::TestStatistics::LikelihoodSerial*/,
+            typename LikelihoodGradientWrapperT /*= RooFit::TestStatistics::LikelihoodGradientSerial*/>
   static std::unique_ptr<RooMinimizer> create(std::shared_ptr<RooFit::TestStatistics::RooAbsL> likelihood);
 
   ~RooMinimizer() override;
@@ -136,10 +136,10 @@ class RooMinimizer : public TObject {
   bool fitFcn() const;
 
 private:
-  template <typename LikelihoodWrapperT = RooFit::TestStatistics::LikelihoodSerial, typename LikelihoodGradientWrapperT = RooFit::TestStatistics::LikelihoodGradientSerial>
+  template <typename LikelihoodWrapperT /*= RooFit::TestStatistics::LikelihoodSerial*/, typename LikelihoodGradientWrapperT /*= RooFit::TestStatistics::LikelihoodGradientSerial*/>
   RooMinimizer(std::shared_ptr<RooFit::TestStatistics::RooAbsL> likelihood,
-               LikelihoodWrapperT* /* used only for template deduction */ = static_cast<RooFit::TestStatistics::LikelihoodSerial*>(nullptr),
-               LikelihoodGradientWrapperT* /* used only for template deduction */ = static_cast<RooFit::TestStatistics::LikelihoodGradientSerial*>(nullptr));
+               LikelihoodWrapperT* /* used only for template deduction = static_cast<RooFit::TestStatistics::LikelihoodSerial*>(nullptr) */,
+               LikelihoodGradientWrapperT* /* used only for template deduction  = static_cast<RooFit::TestStatistics::LikelihoodGradientSerial*>(nullptr) */);
 
   Int_t _printLevel = 1;
   Int_t _status = -99;
diff --git a/roofit/roofitcore/inc/TestStatistics/MinuitFcnGrad.h b/roofit/roofitcore/inc/TestStatistics/MinuitFcnGrad.h
index 5dca9126adc2a..c0752f90d0cb8 100644
--- a/roofit/roofitcore/inc/TestStatistics/MinuitFcnGrad.h
+++ b/roofit/roofitcore/inc/TestStatistics/MinuitFcnGrad.h
@@ -37,7 +37,7 @@ namespace TestStatistics {
 
 // forward declaration
 class LikelihoodSerial;
-class LikelihoodGradientSerial;
+//class LikelihoodGradientSerial;
 
 /// For communication with wrappers, an instance of this struct must be shared between them and MinuitFcnGrad. It keeps
 /// track of what has been evaluated for the current parameter set provided by Minuit.
@@ -56,8 +56,8 @@ struct WrapperCalculationCleanFlags {
 class MinuitFcnGrad : public ROOT::Math::IMultiGradFunction, public RooAbsMinimizerFcn {
 public:
    // factory
-   template <typename LikelihoodWrapperT = RooFit::TestStatistics::LikelihoodSerial,
-             typename LikelihoodGradientWrapperT = RooFit::TestStatistics::LikelihoodGradientSerial>
+   template <typename LikelihoodWrapperT /*= RooFit::TestStatistics::LikelihoodSerial*/,
+             typename LikelihoodGradientWrapperT /*= RooFit::TestStatistics::LikelihoodGradientSerial*/>
    static MinuitFcnGrad *
    create(const std::shared_ptr<RooFit::TestStatistics::RooAbsL> &likelihood, RooMinimizer *context,
           std::vector<ROOT::Fit::ParameterSettings> &parameters, bool verbose = false);