diff --git a/modules/core/test/tools/io/testNPZ.cpp b/modules/core/test/tools/io/testNPZ.cpp
index 98f2b42bc8..ce7006cc06 100644
--- a/modules/core/test/tools/io/testNPZ.cpp
+++ b/modules/core/test/tools/io/testNPZ.cpp
@@ -72,6 +72,9 @@ TEST_CASE("Test visp::cnpy::npy_load/npz_save", "[visp::cnpy I/O]")
   {
     const std::string save_string = "Open Source Visual Servoing Platform";
     std::vector<char> vec_save_string(save_string.begin(), save_string.end());
+    // Manually add a null-terminated character
+    // https://stackoverflow.com/a/8247804
+    vec_save_string.push_back('\0');
     const std::string identifier = "String";
     visp::cnpy::npz_save(npz_filename, identifier, &vec_save_string[0], { vec_save_string.size() }, "w");