diff --git a/libsolidity/formal/SolverInterface.h b/libsolidity/formal/SolverInterface.h
index 8bbd04173..2c4509424 100644
--- a/libsolidity/formal/SolverInterface.h
+++ b/libsolidity/formal/SolverInterface.h
@@ -62,8 +62,6 @@ public:
 
 	Expression(Expression const&) = default;
 	Expression(Expression&&) = default;
-	Expression& operator=(Expression const&) = default;
-	Expression& operator=(Expression&&) = default;
 
 	bool hasCorrectArity() const
 	{