diff --git a/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp b/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp
index cee709a86..5f3857dcd 100644
--- a/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp
+++ b/include/boost/geometry/algorithms/detail/overlay/handle_colocations.hpp
@@ -14,6 +14,7 @@
 #include <map>
 #include <vector>
 
+#include <boost/core/ignore_unused.hpp>
 #include <boost/range.hpp>
 #include <boost/geometry/core/point_order.hpp>
 #include <boost/geometry/algorithms/detail/overlay/cluster_info.hpp>
@@ -396,6 +397,8 @@ inline bool is_ie_turn(segment_identifier const& ext_seg_0,
     bool const same_multi1 = ! Reverse1
                              && ext_seg_1.multi_index == other_seg_1.multi_index;
 
+    boost::ignore_unused(same_multi1);
+
     return same_multi0
             && same_multi1
             && ! is_interior<Reverse0>(ext_seg_0)