diff --git a/src/internal/fsutil.cpp b/src/internal/fsutil.cpp
index 0c9db1e2..04b99f7a 100644
--- a/src/internal/fsutil.cpp
+++ b/src/internal/fsutil.cpp
@@ -307,7 +307,9 @@ auto fsutil::get_file_attributes_ex( const fs::path& filePath,
 
 #if defined( _WIN32 ) && defined( BIT7Z_AUTO_PREFIX_LONG_PATHS )
 
+namespace {
 constexpr auto kLongPathPrefix = BIT7Z_NATIVE_STRING( R"(\\?\)" );
+} // namespace
 
 auto fsutil::should_format_long_path( const fs::path& path ) -> bool {
     constexpr auto kMaxDosFilenameSize = 12;
@@ -316,7 +318,7 @@ auto fsutil::should_format_long_path( const fs::path& path ) -> bool {
         return false;
     }
     const auto& pathStr = path.native();
-    if ( pathStr.size() < ( MAX_PATH - kMaxDosFilenameSize ) ) {
+    if ( pathStr.size() < static_cast<std::size_t>( MAX_PATH - kMaxDosFilenameSize ) ) {
         return false;
     }
     return !starts_with( pathStr, kLongPathPrefix );
@@ -324,6 +326,12 @@ auto fsutil::should_format_long_path( const fs::path& path ) -> bool {
 
 auto fsutil::format_long_path( const fs::path& path ) -> fs::path {
     fs::path longPath = kLongPathPrefix;
+    // Note: we call this function after checking if we should format the given path as a long path.
+    // This means that if the path starts with the \\ prefix,
+    // it is a UNC path and not a long path prefixed with \\?\.
+    if ( starts_with( path.native(), BIT7Z_NATIVE_STRING( R"(\\)" ) ) ) {
+        longPath += L"UNC\\";
+    }
     longPath += path;
     return longPath;
 }
diff --git a/tests/src/test_fsutil.cpp b/tests/src/test_fsutil.cpp
index 1751be27..cbadd328 100644
--- a/tests/src/test_fsutil.cpp
+++ b/tests/src/test_fsutil.cpp
@@ -234,6 +234,40 @@ TEST_CASE( "fsutil: In-archive path computation", "[fsutil][in_archive_path]" )
 
 #endif
 
+#if defined( _WIN32 ) && defined( BIT7Z_AUTO_PREFIX_LONG_PATHS )
+TEST_CASE( "fsutil: Format long Windows paths", "[fsutil][format_long_path]" ) {
+    const std::wstring kLongPathPrefix = BIT7Z_NATIVE_STRING( R"(\\?\)" );
+
+    constexpr auto short_path = L"short_path\\file.txt";
+    REQUIRE_FALSE( should_format_long_path( short_path ) );
+
+    constexpr auto very_long_path = LR"(C:\very\long\dummy\path\)"
+                                    LR"(ABCDEFGHIJKLMNOPQRSTUVWXYZ\abcdefghijklmnopqrstuvwxyz\0123456789\)"
+                                    LR"(Lorem ipsum dolor sit amet\consectetur adipiscing elit\)"
+                                    LR"(Mauris ac leo dui\Morbi non elit lacus\)"
+                                    LR"(Ut ullamcorper sapien eget commodo eleifend\Curabitur varius magna sit\)"
+                                    LR"(Hello_World.txt)";
+    REQUIRE( should_format_long_path( very_long_path ) );
+    REQUIRE( format_long_path( very_long_path ) == ( kLongPathPrefix + very_long_path ) );
+
+
+    const auto prefixed_very_long_path = std::wstring{ LR"(\\?\)" } + very_long_path;
+    REQUIRE_FALSE( should_format_long_path( prefixed_very_long_path ) );
+
+    constexpr auto very_long_unc_path = LR"(\\very\long\dummy\UNC\path\)"
+                                        LR"(ABCDEFGHIJKLMNOPQRSTUVWXYZ\abcdefghijklmnopqrstuvwxyz\0123456789\)"
+                                        LR"(Lorem ipsum dolor sit amet\consectetur adipiscing elit\)"
+                                        LR"(Mauris ac leo dui\Morbi non elit lacus\)"
+                                        LR"(Ut ullamcorper sapien eget commodo eleifend\Curabitur varius magna sit\)"
+                                        LR"(Hello_World.txt)";
+    REQUIRE( should_format_long_path( very_long_unc_path ) );
+    REQUIRE( format_long_path( very_long_unc_path ) == ( kLongPathPrefix + L"UNC\\" + very_long_unc_path ) );
+
+    const auto prefixed_very_long_unc_path = std::wstring{ LR"(\\?\UNC\)" } + very_long_unc_path;
+    REQUIRE_FALSE( should_format_long_path( prefixed_very_long_unc_path ) );
+}
+#endif
+
 #if defined( _WIN32 ) && defined( BIT7Z_PATH_SANITIZATION )
 TEST_CASE( "fsutil: Sanitizing Windows paths", "[fsutil][sanitize_path]" ) {
     REQUIRE( sanitize_path( L"hello world.txt" ) == L"hello world.txt" );