diff --git a/tests/cpp/c_api/test_c_api.cc b/tests/cpp/c_api/test_c_api.cc
index 9a63d51308ec..205e5f561919 100644
--- a/tests/cpp/c_api/test_c_api.cc
+++ b/tests/cpp/c_api/test_c_api.cc
@@ -8,10 +8,11 @@
 #include <xgboost/learner.h>
 #include <xgboost/version_config.h>
 
-#include <array>    // for array
-#include <cstddef>  // std::size_t
-#include <limits>   // std::numeric_limits
-#include <string>   // std::string
+#include <array>      // for array
+#include <cstddef>    // std::size_t
+#include <filesystem> // std::filesystem
+#include <limits>     // std::numeric_limits
+#include <string>     // std::string
 #include <vector>
 
 #include "../../../src/c_api/c_api_error.h"
@@ -162,7 +163,7 @@ TEST(CAPI, ConfigIO) {
 TEST(CAPI, JsonModelIO) {
   size_t constexpr kRows = 10;
   size_t constexpr kCols = 10;
-  dmlc::TemporaryDirectory tempdir;
+  auto tempdir = std::filesystem::temp_directory_path();
 
   auto p_dmat = RandomDataGenerator(kRows, kCols, 0).GenerateDMatrix();
   std::vector<std::shared_ptr<DMatrix>> mat {p_dmat};
@@ -178,19 +179,19 @@ TEST(CAPI, JsonModelIO) {
   learner->UpdateOneIter(0, p_dmat);
   BoosterHandle handle = learner.get();
 
-  std::string modelfile_0 = tempdir.path + "/모델_0.json";
-  XGBoosterSaveModel(handle, modelfile_0.c_str());
-  XGBoosterLoadModel(handle, modelfile_0.c_str());
+  auto modelfile_0 = tempdir / std::filesystem::u8path(u8"모델_0.json");
+  XGBoosterSaveModel(handle, modelfile_0.u8string().c_str());
+  XGBoosterLoadModel(handle, modelfile_0.u8string().c_str());
 
   bst_ulong num_feature {0};
   ASSERT_EQ(XGBoosterGetNumFeature(handle, &num_feature), 0);
   ASSERT_EQ(num_feature, kCols);
 
-  std::string modelfile_1 = tempdir.path + "/model_1.json";
-  XGBoosterSaveModel(handle, modelfile_1.c_str());
+  auto modelfile_1 = tempdir / "model_1.json";
+  XGBoosterSaveModel(handle, modelfile_1.u8string().c_str());
 
-  auto model_str_0 = common::LoadSequentialFile(modelfile_0);
-  auto model_str_1 = common::LoadSequentialFile(modelfile_1);
+  auto model_str_0 = common::LoadSequentialFile(modelfile_0.u8string());
+  auto model_str_1 = common::LoadSequentialFile(modelfile_1.u8string());
 
   ASSERT_EQ(model_str_0.front(), '{');
   ASSERT_EQ(model_str_0, model_str_1);