diff --git a/Core/FormFactors/FormFactorPolyhedron.h b/Core/FormFactors/FormFactorPolyhedron.h
index f1b327a07c6b09a03c3cd8cac4626c0b2ba9f069..a848cffb9200dc462cf94457b9398d2c52dfe0df 100644
--- a/Core/FormFactors/FormFactorPolyhedron.h
+++ b/Core/FormFactors/FormFactorPolyhedron.h
@@ -109,6 +109,7 @@ public:
 
     FormFactorPolyhedron() {}
 
+    virtual void onChange() = 0;
     virtual complex_t evaluate_for_q(const cvector_t q ) const final;
     complex_t evaluate_centered( const cvector_t q ) const;