diff --git a/Framework/ProcessSequence/testProcessSequence.cc b/Framework/ProcessSequence/testProcessSequence.cc
index 552eb01a1a012b68cad7ce864476f74d64f3564a..b51876886acbd22a80dd20aca4abe5d50c23e216 100644
--- a/Framework/ProcessSequence/testProcessSequence.cc
+++ b/Framework/ProcessSequence/testProcessSequence.cc
@@ -147,7 +147,7 @@ public:
 class Decay1 : public DecayProcess<Decay1> {
 
 public:
-  Decay1(const int v) {
+  Decay1(const int) {
     cout << "Decay1()" << endl;
     globalCount++;
   }
diff --git a/Framework/StackInterface/SecondaryView.h b/Framework/StackInterface/SecondaryView.h
index 572a57f06dd923c952a9929b191b2e3414ac8c8e..ea350463c11868b465ec07f76cce88d7519af063 100644
--- a/Framework/StackInterface/SecondaryView.h
+++ b/Framework/StackInterface/SecondaryView.h
@@ -17,6 +17,10 @@
 
 namespace corsika::stack {
 
+  // forward-decl:
+  template <class T1, template <class> class T2>
+  class DefaultSecondaryProducer;
+
   /**
    * @class SecondaryView
    *
@@ -57,7 +61,7 @@ namespace corsika::stack {
 
   template <typename StackDataType,
             template <typename> typename ParticleInterface,
-            template <class T1, template <class> class T2> class MSecondaryProducer>
+            template <class T1, template <class> class T2> class MSecondaryProducer = DefaultSecondaryProducer>
 
   class SecondaryView : public Stack<StackDataType&, ParticleInterface>,
                         public MSecondaryProducer<StackDataType, ParticleInterface> {