diff --git a/doc/python-spglib.md b/doc/python-spglib.md
index 694801ee0..2c0ae028c 100644
--- a/doc/python-spglib.md
+++ b/doc/python-spglib.md
@@ -595,8 +595,9 @@ Arguments
 - `mag_symprec`: See {ref}`py_get_magnetic_symmetry`
 - `is_axial`: See {ref}`py_get_magnetic_symmetry`
 
-Returned `dataset` is a dictionary.
+If successful, returned `dataset` is a dictionary.
 The description of its keys is given at {ref}`magnetic_spglib_dataset`.
+If the magnetic symmetry search failed, `dataset` is `None`.
 
 ### `get_magnetic_spacegroup_type`
 
diff --git a/src/magnetic_spacegroup.c b/src/magnetic_spacegroup.c
index ab517b36b..eac710d0b 100644
--- a/src/magnetic_spacegroup.c
+++ b/src/magnetic_spacegroup.c
@@ -439,6 +439,9 @@ static int get_reference_space_group(Spacegroup **ref_sg,
     type = get_magnetic_space_group_type(&representatives, magnetic_symmetry,
                                          sym_fsg->size, sym_xsg->size);
     debug_print("type=%d\n", type);
+    if (type == 0) {
+        goto err;
+    }
 
     /* Choose reference setting */
     /* For type-IV, use setting from Hall symbol of XSG. */
diff --git a/test/README.md b/test/README.md
index 22423a880..9d2f68e9e 100644
--- a/test/README.md
+++ b/test/README.md
@@ -12,9 +12,11 @@ For example, to run `test_symmetry_search.test_spg_get_symmetry`
 
 ```shell
 # at build/test
-./CTests --gtest_filter=test_spg_get_symmetry
+./CTests --gtest_filter=test_symmetry_search.test_spg_get_symmetry
 ```
 
+If you use debuggers like gdb or lldb, recompile with `CMAKE_BUILD_TYPE=Debug`.
+
 ## How to add a new test file
 
 1. Create `<your_test_suite_name>.cpp`
diff --git a/test/test_magnetic_symmetry.cpp b/test/test_magnetic_symmetry.cpp
index 233f23125..188eaf016 100644
--- a/test/test_magnetic_symmetry.cpp
+++ b/test/test_magnetic_symmetry.cpp
@@ -364,6 +364,71 @@ TEST(test_magnetic_symmetry, test_spg_get_symmetry_with_tensors_rough_symprec) {
     free(time_reversals);
 }
 
+TEST(test_magnetic_symmetry, test_spgms_get_magnetic_dataset_high_mag_symprec) {
+    // https://github.com/spglib/spglib/issues/249
+    double lattice[3][3] = {
+        {0.00000000, -5.00000000, -2.50000000},
+        {0.00000000, 0.00000000, 4.33012702},
+        {-4.05000000, 0.00000000, 0.00000000},
+    };
+    double positions[][3] = {
+        {0.50000000, 0.33333333, 0.33333333},
+        {0.50000000, 0.66666667, 0.66666667},
+        {0.00000000, 0.00000000, 0.00000000},
+        {0.00000000, 0.00000000, 0.50000000},
+        {0.00000000, 0.50000000, 0.50000000},
+        {0.00000000, 0.50000000, 0.00000000},
+    };
+    int types[] = {1, 1, 1, 2, 2, 2};
+    double tensors[] = {
+        -0.00200000, 0.00200000,  1.90000000,  0.00200000,  0.00000000,
+        1.91100000,  -0.00100000, 0.00200000,  -2.23300000, -0.00000000,
+        -0.00000000, -0.06000000, 0.00000000,  0.00000000,  -0.03200000,
+        0.00000000,  -0.00000000, -0.02900000,
+    };
+    int num_atoms = 6;
+
+    int max_size = num_atoms * 96;
+
+    double symprec = 1e-5;
+    double mag_symprec = 1e-1;  // with high mag_symprec
+
+    int i, size;
+    int equivalent_atoms[3];
+    double primitive_lattice[3][3];
+    int(*rotations)[3][3];
+    double(*translations)[3];
+    int *spin_flips;
+    int *time_reversals;
+
+    rotations = (int(*)[3][3])malloc(sizeof(int[3][3]) * max_size);
+    translations = (double(*)[3])malloc(sizeof(double[3]) * max_size);
+    spin_flips = (int *)malloc(sizeof(int *) * max_size);
+    time_reversals = (int *)malloc(sizeof(int *) * max_size);
+
+    size = spgms_get_symmetry_with_site_tensors(
+        rotations, translations, equivalent_atoms, primitive_lattice,
+        spin_flips, max_size, lattice, positions, types, tensors,
+        1 /* tensor_rank */, num_atoms, 1 /* with_time_reversal */,
+        1 /* is_axial */, symprec, -1 /* angle_tolerance */, mag_symprec);
+    // spgms_get_symmetry_with_site_tensors should return one or more symmetry
+    // operations
+    ASSERT_TRUE(size > 0);
+
+    SpglibMagneticDataset *dataset;
+    dataset =
+        spgms_get_magnetic_dataset(lattice, positions, types, tensors, 1,
+                                   num_atoms, 1, symprec, -1, mag_symprec);
+    // MSG identification is failed with the too high mag_symprec
+    ASSERT_TRUE(dataset == NULL);
+
+    free(rotations);
+    free(translations);
+    free(spin_flips);
+    free(time_reversals);
+    if (dataset != NULL) spg_free_magnetic_dataset(dataset);
+}
+
 TEST(test_magnetic_symmetry, test_with_broken_symmetry) {
     // https://github.com/spglib/spglib/issues/194
     // Part of "mp-806965" in the Materials Project database