diff --git a/include/xcdat.hpp b/include/xcdat.hpp
index 7189d43..d59b57f 100644
--- a/include/xcdat.hpp
+++ b/include/xcdat.hpp
@@ -13,14 +13,14 @@ namespace xcdat {
 using trie_7_type = trie<bc_vector_7>;
 using trie_8_type = trie<bc_vector_8>;
 
-using flag_type = std::remove_const_t<decltype(trie_7_type::l1_bits)>;
-
 template <class Trie>
 [[maybe_unused]] Trie mmap(const char* address) {
     mmap_visitor visitor(address);
-    flag_type flag;
+
+    std::uint32_t flag;
     visitor.visit(flag);
     XCDAT_THROW_IF(flag != Trie::l1_bits, "The input index type is different.");
+
     Trie idx;
     visitor.visit(idx);
     return idx;
@@ -29,9 +29,11 @@ template <class Trie>
 template <class Trie>
 [[maybe_unused]] Trie load(std::string_view filepath) {
     load_visitor visitor(filepath);
-    flag_type flag;
+
+    std::uint32_t flag;
     visitor.visit(flag);
     XCDAT_THROW_IF(flag != Trie::l1_bits, "The input index type is different.");
+
     Trie idx;
     visitor.visit(idx);
     return idx;
@@ -40,7 +42,7 @@ template <class Trie>
 template <class Trie>
 [[maybe_unused]] std::uint64_t save(const Trie& idx, std::string_view filepath) {
     save_visitor visitor(filepath);
-    visitor.visit(Trie::l1_bits);  // flag
+    visitor.visit(static_cast<std::uint32_t>(Trie::l1_bits));  // flag
     visitor.visit(const_cast<Trie&>(idx));
     return visitor.bytes();
 }
@@ -48,11 +50,20 @@ template <class Trie>
 template <class Trie>
 [[maybe_unused]] std::uint64_t memory_in_bytes(const Trie& idx) {
     size_visitor visitor;
-    visitor.visit(Trie::l1_bits);  // flag
+    visitor.visit(static_cast<std::uint32_t>(Trie::l1_bits));  // flag
     visitor.visit(const_cast<Trie&>(idx));
     return visitor.bytes();
 }
 
+[[maybe_unused]] std::uint32_t get_flag(std::string_view filepath) {
+    std::ifstream ifs(filepath);
+    XCDAT_THROW_IF(!ifs.good(), "Cannot open the input file");
+
+    std::uint32_t flag;
+    ifs.read(reinterpret_cast<char*>(&flag), sizeof(flag));
+    return flag;
+}
+
 [[maybe_unused]] std::vector<std::string> load_strings(std::string_view filepath) {
     std::ifstream ifs(filepath);
     if (!ifs) {
diff --git a/tools/xcdat_decode.cpp b/tools/xcdat_decode.cpp
index d6d30c3..25d77d0 100644
--- a/tools/xcdat_decode.cpp
+++ b/tools/xcdat_decode.cpp
@@ -10,14 +10,6 @@ cmd_line_parser::parser make_parser(int argc, char** argv) {
     return p;
 }
 
-xcdat::flag_type get_flag(std::string_view filepath) {
-    std::ifstream ifs(filepath);
-    XCDAT_THROW_IF(!ifs.good(), "Cannot open the input file");
-    xcdat::flag_type flag;
-    ifs.read(reinterpret_cast<char*>(&flag), sizeof(flag));
-    return flag;
-}
-
 template <class Trie>
 int decode(const cmd_line_parser::parser& p) {
     const auto input_idx = p.get<std::string>("input_idx");
@@ -45,7 +37,7 @@ int main(int argc, char** argv) {
     }
 
     const auto input_idx = p.get<std::string>("input_idx");
-    const auto flag = get_flag(input_idx);
+    const auto flag = xcdat::get_flag(input_idx);
 
     switch (flag) {
         case 7:
diff --git a/tools/xcdat_enumerate.cpp b/tools/xcdat_enumerate.cpp
index cd4b99e..9316211 100644
--- a/tools/xcdat_enumerate.cpp
+++ b/tools/xcdat_enumerate.cpp
@@ -10,14 +10,6 @@ cmd_line_parser::parser make_parser(int argc, char** argv) {
     return p;
 }
 
-xcdat::flag_type get_flag(std::string_view filepath) {
-    std::ifstream ifs(filepath);
-    XCDAT_THROW_IF(!ifs.good(), "Cannot open the input file");
-    xcdat::flag_type flag;
-    ifs.read(reinterpret_cast<char*>(&flag), sizeof(flag));
-    return flag;
-}
-
 template <class Trie>
 int enumerate(const cmd_line_parser::parser& p) {
     const auto input_idx = p.get<std::string>("input_idx");
@@ -42,7 +34,7 @@ int main(int argc, char** argv) {
     }
 
     const auto input_idx = p.get<std::string>("input_idx");
-    const auto flag = get_flag(input_idx);
+    const auto flag = xcdat::get_flag(input_idx);
 
     switch (flag) {
         case 7:
diff --git a/tools/xcdat_lookup.cpp b/tools/xcdat_lookup.cpp
index d06d738..ed68298 100644
--- a/tools/xcdat_lookup.cpp
+++ b/tools/xcdat_lookup.cpp
@@ -10,14 +10,6 @@ cmd_line_parser::parser make_parser(int argc, char** argv) {
     return p;
 }
 
-xcdat::flag_type get_flag(std::string_view filepath) {
-    std::ifstream ifs(filepath);
-    XCDAT_THROW_IF(!ifs.good(), "Cannot open the input file");
-    xcdat::flag_type flag;
-    ifs.read(reinterpret_cast<char*>(&flag), sizeof(flag));
-    return flag;
-}
-
 template <class Trie>
 int lookup(const cmd_line_parser::parser& p) {
     const auto input_idx = p.get<std::string>("input_idx");
@@ -49,7 +41,7 @@ int main(int argc, char** argv) {
     }
 
     const auto input_idx = p.get<std::string>("input_idx");
-    const auto flag = get_flag(input_idx);
+    const auto flag = xcdat::get_flag(input_idx);
 
     switch (flag) {
         case 7:
diff --git a/tools/xcdat_predictive_search.cpp b/tools/xcdat_predictive_search.cpp
index 00f1130..39195fa 100644
--- a/tools/xcdat_predictive_search.cpp
+++ b/tools/xcdat_predictive_search.cpp
@@ -11,14 +11,6 @@ cmd_line_parser::parser make_parser(int argc, char** argv) {
     return p;
 }
 
-xcdat::flag_type get_flag(std::string_view filepath) {
-    std::ifstream ifs(filepath);
-    XCDAT_THROW_IF(!ifs.good(), "Cannot open the input file");
-    xcdat::flag_type flag;
-    ifs.read(reinterpret_cast<char*>(&flag), sizeof(flag));
-    return flag;
-}
-
 template <class Trie>
 int predictive_search(const cmd_line_parser::parser& p) {
     const auto input_idx = p.get<std::string>("input_idx");
@@ -64,7 +56,7 @@ int main(int argc, char** argv) {
     }
 
     const auto input_idx = p.get<std::string>("input_idx");
-    const auto flag = get_flag(input_idx);
+    const auto flag = xcdat::get_flag(input_idx);
 
     switch (flag) {
         case 7:
diff --git a/tools/xcdat_prefix_search.cpp b/tools/xcdat_prefix_search.cpp
index ac2f81b..41141c6 100644
--- a/tools/xcdat_prefix_search.cpp
+++ b/tools/xcdat_prefix_search.cpp
@@ -10,14 +10,6 @@ cmd_line_parser::parser make_parser(int argc, char** argv) {
     return p;
 }
 
-xcdat::flag_type get_flag(std::string_view filepath) {
-    std::ifstream ifs(filepath);
-    XCDAT_THROW_IF(!ifs.good(), "Cannot open the input file");
-    xcdat::flag_type flag;
-    ifs.read(reinterpret_cast<char*>(&flag), sizeof(flag));
-    return flag;
-}
-
 template <class Trie>
 int prefix_search(const cmd_line_parser::parser& p) {
     const auto input_idx = p.get<std::string>("input_idx");
@@ -62,7 +54,7 @@ int main(int argc, char** argv) {
     }
 
     const auto input_idx = p.get<std::string>("input_idx");
-    const auto flag = get_flag(input_idx);
+    const auto flag = xcdat::get_flag(input_idx);
 
     switch (flag) {
         case 7: