diff --git a/include/internal/catch_expression_lhs.hpp b/include/internal/catch_expression_lhs.hpp
index 33a0cb11..106a6b0a 100644
--- a/include/internal/catch_expression_lhs.hpp
+++ b/include/internal/catch_expression_lhs.hpp
@@ -27,6 +27,8 @@ class ExpressionLhs : public DecomposedExpression {
 public:
     ExpressionLhs( ResultBuilder& rb, T lhs ) : m_rb( rb ), m_lhs( lhs ), m_truthy(false) {}
 
+    ExpressionLhs& operator = ( const ExpressionLhs& );
+
     template<typename RhsT>
     BinaryExpression<T, Internal::IsEqualTo, RhsT const&>
     operator == ( RhsT const& rhs ) {
@@ -105,6 +107,8 @@ public:
     BinaryExpression( ResultBuilder& rb, LhsT lhs, RhsT rhs )
         : m_rb( rb ), m_lhs( lhs ), m_rhs( rhs ) {}
 
+    BinaryExpression& operator = ( BinaryExpression& );
+
     void endExpression() const {
         m_rb
             .setResultType( Internal::compare<Op>( m_lhs, m_rhs ) )