diff --git a/Helicity/Vertex/AbstractSSSSVertex.cc b/Helicity/Vertex/AbstractSSSSVertex.cc
--- a/Helicity/Vertex/AbstractSSSSVertex.cc
+++ b/Helicity/Vertex/AbstractSSSSVertex.cc
@@ -1,26 +1,32 @@
 // -*- C++ -*-
 //
 // This is the implementation of the non-inlined, non-templated member
 // functions of the AbstractSSSSVertex class.
 //
 
 #include "AbstractSSSSVertex.h"
 #include "ThePEG/Utilities/DescribeClass.h"
 #include "ThePEG/Interface/ClassDocumentation.h"
 
 using namespace ThePEG;
 using namespace Helicity;
 
 // The following static variable is needed for the type
 // description system in ThePEG.
 DescribeAbstractNoPIOClass<AbstractSSSSVertex,VertexBase>
 describeThePEGAbstractSSSSVertex("ThePEG::AbstractSSSSVertex", "libThePEG.so");
 
 void AbstractSSSSVertex::Init() {
 
   static ClassDocumentation<AbstractSSSSVertex> documentation
     ("The AbstractSSSSVertex class is the base class for all "
      "scalar-scalar-scalar-scalar interactions");
 
 }
 
+ScalarWaveFunction AbstractSSSSVertex::evaluate(Energy2,int, tcPDPtr, 
+						const ScalarWaveFunction & ,
+						const ScalarWaveFunction & ,
+						const ScalarWaveFunction & ) {
+  assert(false);
+}
diff --git a/Helicity/Vertex/AbstractSSSSVertex.h b/Helicity/Vertex/AbstractSSSSVertex.h
--- a/Helicity/Vertex/AbstractSSSSVertex.h
+++ b/Helicity/Vertex/AbstractSSSSVertex.h
@@ -1,88 +1,88 @@
 // -*- C++ -*-
 #ifndef HELICITY_AbstractSSSSVertex_H
 #define HELICITY_AbstractSSSSVertex_H
 //
 // This is the declaration of the AbstractSSSSVertex class.
 //
 
 #include "VertexBase.h"
 #include "ThePEG/Helicity/WaveFunction/ScalarWaveFunction.h"
 #include "AbstractSSSSVertex.fh"
 
 namespace ThePEG {
 namespace Helicity {
 
 /**
  * The AbstractSSSSVertex class is the base class for all scalar-scalar-scalar
  * interactions in ThePEG
  */
 class AbstractSSSSVertex: public VertexBase {
 
 public:
 
   /**
    * Default constructor
    */
   AbstractSSSSVertex() : VertexBase(VertexType::SSSS) {}
 
   /**
    * Members to calculate the helicity amplitude expressions for vertices
    * and off-shell particles.
    */
   //@{  
   /**
    * Evaluate the vertex.
    * @param q2 The scale \f$q^2\f$ for the coupling at the vertex.
    * @param sca1 The wavefunction for the first  scalar.
    * @param sca2 The wavefunction for the second scalar.
    * @param sca3 The wavefunction for the third  scalar.
    * @param sca4 The wavefunction for the fourth scalar.
    */
   virtual Complex evaluate(Energy2 q2,const ScalarWaveFunction & sca1,
 			   const ScalarWaveFunction & sca2,
 			   const ScalarWaveFunction & sca3,
 			   const ScalarWaveFunction & sca4) = 0;
 
   /**
    * Evaluate the off-shell scalar coming from the vertex.
    * @param q2 The scale \f$q^2\f$ for the coupling at the vertex.
    * @param iopt Option of the shape of the Breit-Wigner for the off-shell scalar.
    * @param out The ParticleData pointer for the off-shell scalar.
    * @param sca1 The wavefunction for the first  scalar.
    * @param sca2 The wavefunction for the second scalar.
    * @param sca3 The wavefunction for the third  scalar.
    */
   virtual ScalarWaveFunction evaluate(Energy2 q2,int iopt, tcPDPtr out, 
 				      const ScalarWaveFunction & sca1,
 				      const ScalarWaveFunction & sca2,
-				      const ScalarWaveFunction & sca3) = 0;
+				      const ScalarWaveFunction & sca3);
   //@}
 
 public:
 
   /**
    * The standard Init function used to initialize the interfaces.
    * Called exactly once for each class by the class description system
    * before the main function starts or
    * when this class is dynamically loaded.
    */
   static void Init();
 
 private:
 
   /**
    * The assignment operator is private and must never be called.
    * In fact, it should not even be implemented.
    */
   AbstractSSSSVertex & operator=(const AbstractSSSSVertex &) = delete;
 
 };
 
 }
 }
 
 
 namespace ThePEG {
 
 }
 #endif /* HELICITY_AbstractSSSSVertex_H */