diff --git a/GMLMIP-0.1/formulas/formula.h b/GMLMIP-0.1/formulas/formula.h
index a5931d1497c1b2cfd0d3b7f08c9eeed1ef80933d..3cc0372321d3a7b555b46049c55f124704dfb4bf 100644
--- a/GMLMIP-0.1/formulas/formula.h
+++ b/GMLMIP-0.1/formulas/formula.h
@@ -41,6 +41,7 @@ class IFormula {
 		virtual bdd modal(bdd *b, int n, int m)=0;
 		virtual bool satisfiability(int option)=0;
 		virtual void clear_maps()=0;
+		virtual ~IFormula() { };
 };
 
 template<class ModalValueType>