diff --git a/swig/libcclexpression.i b/swig/libcclexpression.i
index b401e859ee380a0b911092228eb12d6babccc89a..128f7a9f0492a0a05defd21bab6d3d501b54e14b 100644
--- a/swig/libcclexpression.i
+++ b/swig/libcclexpression.i
@@ -14,6 +14,7 @@ namespace Wccl {
   class Expression : boost::noncopyable {
   public:
     virtual std::string to_string(const Corpus2::Tagset& tagset) const = 0;
+    std::string to_raw_string() const;
   };
 }