diff --git a/Framework/Geometry/inc/MantidGeometry/Crystal/HKLGenerator.h b/Framework/Geometry/inc/MantidGeometry/Crystal/HKLGenerator.h
index 5c4259677314690be059cfb72b1d252d8f5e19c8..f004bb8fccadfdf12b14daa5fc935d97b93926b1 100644
--- a/Framework/Geometry/inc/MantidGeometry/Crystal/HKLGenerator.h
+++ b/Framework/Geometry/inc/MantidGeometry/Crystal/HKLGenerator.h
@@ -109,7 +109,7 @@ public:
    * While the iterators can be instantiated directly, the intention is to
    * use HKLGenerator::begin() and HKLGenerator::end().
    */
-  class const_iterator
+  class MANTID_GEOMETRY_DLL const_iterator
       : public boost::iterator_facade<const_iterator, const Kernel::V3D &,
                                       boost::forward_traversal_tag> {
   public: