diff --git a/src/gmio_core/internal/zip_utils.c b/src/gmio_core/internal/zip_utils.c
index fa5f209..686d327 100644
--- a/src/gmio_core/internal/zip_utils.c
+++ b/src/gmio_core/internal/zip_utils.c
@@ -161,7 +161,7 @@ size_t gmio_zip_read_local_file_header(
         int *ptr_error)
 {
     uint8_t buff[GMIO_ZIP_SIZE_LOCAL_FILE_HEADER];
-    uint8_t* buffit = buff;
+    const uint8_t* buffit = buff;
 
     const size_t read_len = gmio_stream_read_bytes(stream, buff, sizeof(buff));
     if (!gmio_zip_read_checkhelper(stream, read_len, sizeof(buff)))
@@ -251,7 +251,7 @@ size_t gmio_zip_read_central_directory_header(
         int *ptr_error)
 {
     uint8_t buff[GMIO_ZIP_SIZE_CENTRAL_DIRECTORY_HEADER];
-    uint8_t* buffit = buff;
+    const uint8_t* buffit = buff;
 
     const size_t read_len = gmio_stream_read_bytes(stream, buff, sizeof(buff));
     if (!gmio_zip_read_checkhelper(stream, read_len, sizeof(buff)))
@@ -311,7 +311,7 @@ size_t gmio_zip_read_end_of_central_directory_record(
         int *ptr_error)
 {
     uint8_t buff[GMIO_ZIP_SIZE_END_OF_CENTRAL_DIRECTORY_RECORD];
-    uint8_t* buffit = buff;
+    const uint8_t* buffit = buff;
 
     const size_t read_len = gmio_stream_read_bytes(stream, buff, sizeof(buff));
     if (!gmio_zip_read_checkhelper(stream, read_len, sizeof(buff)))
@@ -404,7 +404,7 @@ size_t gmio_zip_read_data_descriptor(
         int* ptr_error)
 {
     uint8_t buff[GMIO_ZIP_SIZE_DATA_DESCRIPTOR];
-    uint8_t* buffit = buff;
+    const uint8_t* buffit = buff;
 
     const size_t read_len = gmio_stream_read_bytes(stream, buff, sizeof(buff));
     if (!gmio_zip_read_checkhelper(stream, read_len, sizeof(buff)))
@@ -427,7 +427,7 @@ size_t gmio_zip64_read_data_descriptor(
 {
 #ifdef GMIO_HAVE_INT64_TYPE
     uint8_t buff[GMIO_ZIP64_SIZE_DATA_DESCRIPTOR];
-    uint8_t* buffit = buff;
+    const uint8_t* buffit = buff;
 
     const size_t read_len = gmio_stream_read_bytes(stream, buff, sizeof(buff));
     if (!gmio_zip_read_checkhelper(stream, read_len, sizeof(buff)))
diff --git a/src/gmio_core/internal/zip_utils.h b/src/gmio_core/internal/zip_utils.h
index 1adbb2d..b085f07 100644
--- a/src/gmio_core/internal/zip_utils.h
+++ b/src/gmio_core/internal/zip_utils.h
@@ -246,7 +246,7 @@ struct gmio_zip_write_result {
     size_t written_len;
 };
 
-enum { GMIO_ZIP_UTILS_ERROR_TAG = 0xAA000000 };
+enum { GMIO_ZIP_UTILS_ERROR_TAG = 0x00AA0000 };
 enum gmio_zip_utils_error {
     GMIO_ZIP_UTILS_ERROR_BAD_MAGIC = GMIO_ZIP_UTILS_ERROR_TAG + 0x01
 };
diff --git a/tests/test_stl_io.c b/tests/test_stl_io.c
index 845689d..7a6c70e 100644
--- a/tests/test_stl_io.c
+++ b/tests/test_stl_io.c
@@ -151,7 +151,6 @@ static const char* test_stlb_header_write()
     const char* filepath = "temp/solid.stlb";
     struct gmio_stlb_header header = {0};
     const char* header_str = "temp/solid.stlb generated with gmio library";
-    int error = GMIO_ERROR_OK;
 
     {
         FILE* outfile = fopen(filepath, "wb");
@@ -159,7 +158,7 @@ static const char* test_stlb_header_write()
         memcpy(&header,
                header_str,
                GMIO_MIN(GMIO_STLB_HEADER_SIZE, strlen(header_str)));
-        error = gmio_stlb_header_write(
+        const int error = gmio_stlb_header_write(
                     &stream, GMIO_ENDIANNESS_LITTLE, &header, 0);
         fclose(outfile);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
@@ -168,7 +167,7 @@ static const char* test_stlb_header_write()
     {
         struct gmio_stl_data data = {0};
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data);
-        error = gmio_stl_read_file(filepath, &creator, NULL);
+        const int error = gmio_stl_read_file(filepath, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
         UTEST_ASSERT(gmio_stlb_header_equal(&header, &data.header));
         UTEST_COMPARE_UINT(0, data.tri_array.count);
@@ -192,12 +191,11 @@ static const char* test_stlb_write()
     const char* model_fpath_out = "temp/solid.le_stlb";
     const char* model_fpath_out_be = "temp/solid.be_stlb";
     struct gmio_stl_data data = {0};
-    int error = GMIO_ERROR_OK;
 
     /* Read input model file */
     {
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data);
-        error = gmio_stl_read_file(model_fpath, &creator, NULL);
+        const int error = gmio_stl_read_file(model_fpath, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
 
@@ -208,13 +206,14 @@ static const char* test_stlb_write()
         const struct gmio_stl_mesh mesh = gmio_stl_data_mesh(&data);
         struct gmio_stl_write_options opts = {0};
         opts.stlb_header = data.header;
-        error = gmio_stl_write_file(
+        int error = gmio_stl_write_file(
                     GMIO_STL_FORMAT_BINARY_LE, model_fpath_out, &mesh, &opts);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
 
         /* Big-endian version */
         error = gmio_stl_write_file(
                     GMIO_STL_FORMAT_BINARY_BE, model_fpath_out_be, &mesh, &opts);
+        UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
 
     /* Check input and output models are equal */
@@ -251,7 +250,7 @@ static const char* test_stlb_write()
     {
         struct gmio_stl_data data_be = {0};
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data_be);
-        error = gmio_stl_read_file(model_fpath_out_be, &creator, NULL);
+        const int error = gmio_stl_read_file(model_fpath_out_be, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
         UTEST_ASSERT(gmio_stlb_header_equal(&data.header, &data_be.header));
         UTEST_COMPARE_UINT(data.tri_array.count, data_be.tri_array.count);
@@ -273,12 +272,11 @@ static const char* test_stla_write()
     const char* model_filepath_out = "temp/solid.stla";
     struct gmio_stl_data data = {0}; /* TODO: fix memory leak on error */
     char header_str[GMIO_STLB_HEADER_SIZE + 1] = {0};
-    int error = GMIO_ERROR_OK;
 
     /* Read input model file */
     {
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data);
-        error = gmio_stl_read_file(model_filepath, &creator, NULL);
+        const int error = gmio_stl_read_file(model_filepath, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
 
@@ -290,7 +288,7 @@ static const char* test_stla_write()
         opts.stla_solid_name = header_str;
         opts.stla_float32_prec = 7;
         opts.stla_float32_format = GMIO_FLOAT_TEXT_FORMAT_SHORTEST_LOWERCASE;
-        error = gmio_stl_write_file(
+        const int error = gmio_stl_write_file(
                     GMIO_STL_FORMAT_ASCII, model_filepath_out, &mesh, &opts);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
@@ -301,18 +299,17 @@ static const char* test_stla_write()
         struct gmio_stl_data data_stla = {0};
         struct gmio_stl_mesh_creator creator =
                 gmio_stl_data_mesh_creator(&data_stla);
-        size_t i = 0;
         gmio_cstr_copy(
                     trim_header_str,
                     sizeof(trim_header_str),
                     header_str,
                     sizeof(header_str));
         gmio_string_trim_from_end(trim_header_str, sizeof(header_str));
-        error = gmio_stl_read_file(model_filepath_out, &creator, NULL);
+        const int error = gmio_stl_read_file(model_filepath_out, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
         UTEST_COMPARE_UINT(data.tri_array.count, data_stla.tri_array.count);
         UTEST_COMPARE_CSTR(trim_header_str, data_stla.solid_name);
-        for (i = 0; i < data.tri_array.count; ++i) {
+        for (size_t i = 0; i < data.tri_array.count; ++i) {
             const struct gmio_stl_triangle* lhs = &data.tri_array.ptr[i];
             const struct gmio_stl_triangle* rhs = &data_stla.tri_array.ptr[i];
             const bool tri_equal = gmio_stl_triangle_equal(lhs, rhs, 5);
@@ -369,7 +366,7 @@ static const char* test_stla_lc_numeric()
     int error[4] = {0};
 
     gmio_lc_numeric_save();
-    setlocale(LC_NUMERIC, "");
+    setlocale(LC_NUMERIC, ""); /* "" -> environment's default locale */
     if (!gmio_lc_numeric_is_C()) {
         struct gmio_stl_read_options read_opts = {0};
         struct gmio_stl_write_options write_opts = {0};
@@ -381,17 +378,14 @@ static const char* test_stla_lc_numeric()
         error[2] = gmio_stla_read(&null_stream, &null_meshcreator, &read_opts);
         error[3] = gmio_stl_write(
                     GMIO_STL_FORMAT_ASCII, &null_stream, &null_mesh, &write_opts);
-    }
-    else {
-        fprintf(stderr, "\nskip: default locale is NULL or already C/POSIX");
-    }
-    gmio_lc_numeric_restore();
-    {
-        size_t i = 0;
-        for (; i < GMIO_ARRAY_SIZE(error); ++i) {
+        for (size_t i = 0; i < GMIO_ARRAY_SIZE(error); ++i) {
             UTEST_COMPARE_INT(GMIO_ERROR_BAD_LC_NUMERIC, error[i]);
         }
     }
+    else {
+        fprintf(stderr, "\nskip: default locale is NULL or already C/POSIX\n");
+    }
+    gmio_lc_numeric_restore();
 
     return NULL;
 }