diff --git a/tutorial/tracking/model-based/generic/tutorial-mb-generic-tracker-save.cpp b/tutorial/tracking/model-based/generic/tutorial-mb-generic-tracker-save.cpp
index efd53106c7..4fac889d96 100644
--- a/tutorial/tracking/model-based/generic/tutorial-mb-generic-tracker-save.cpp
+++ b/tutorial/tracking/model-based/generic/tutorial-mb-generic-tracker-save.cpp
@@ -138,7 +138,7 @@ int main(int argc, char **argv)
   vec_img_data.reserve(g.getLastFrameIndex() * height * width);
 
   std::vector<double> times;
-  int iter = 0;
+  size_t iter = 0;
   while (!g.end()) {
     g.acquire(I);
     tracker.track(I);
@@ -175,14 +175,14 @@ int main(int argc, char **argv)
     tracker.getModelForDisplay(mapOfModels, mapOfW, mapOfH, mapOfcMos, mapOfCams);
 
     std::vector<std::vector<double>> model = mapOfModels[camera_name];
-    const std::string model_iter = toString("model_%06d", iter);
+    const std::string model_iter = toString("model_%06zu", iter);
     const std::string model_iter_sz = model_iter + "_sz";
     const size_t model_size = model.size();
     visp::cnpy::npz_save(npz_filename, model_iter_sz, &model_size, { 1 }, "a");
 
     for (size_t i = 0; i < model.size(); i++) {
       char buffer[100];
-      int res = snprintf(buffer, 100, "model_%06d_%06zu", iter, i);
+      int res = snprintf(buffer, 100, "model_%06zu_%06zu", iter, i);
       if (res > 0 && res < 100) {
         const std::string model_iter_data = buffer;
         std::vector<double> &vec_line = model[i];