diff --git a/Classification/examples/Classification/gis_tutorial_example.cpp b/Classification/examples/Classification/gis_tutorial_example.cpp
index 62686301d76..2c3b1061c89 100644
--- a/Classification/examples/Classification/gis_tutorial_example.cpp
+++ b/Classification/examples/Classification/gis_tutorial_example.cpp
@@ -669,7 +669,7 @@ int main (int argc, char** argv)
   }
 
   std::size_t nb_vertices
-    = std::accumulate (polylines.begin(), polylines.end(), 0,
+    = std::accumulate (polylines.begin(), polylines.end(), 0u,
                        [](std::size_t size, const std::vector<Point_3>& poly) -> std::size_t
                        { return size + poly.size(); });