diff --git a/src/extra/nnue_data_binpack_format.h b/src/extra/nnue_data_binpack_format.h
index 2c555939..7ceafbc0 100644
--- a/src/extra/nnue_data_binpack_format.h
+++ b/src/extra/nnue_data_binpack_format.h
@@ -41,6 +41,7 @@ THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <array>
 #include <limits>
 #include <climits>
+#include <optional>
 
 #if (defined(_MSC_VER) || defined(__INTEL_COMPILER)) && !defined(__clang__)
 #include <intrin.h>
@@ -7196,4 +7197,4 @@ namespace binpack
 
         std::cout << "Finished. Converted " << numProcessedPositions << " positions.\n";
     }
-}
\ No newline at end of file
+}