diff --git a/include/ceres/internal/autodiff.h b/include/ceres/internal/autodiff.h
index 29a17d8..f00e537 100644
--- a/include/ceres/internal/autodiff.h
+++ b/include/ceres/internal/autodiff.h
@@ -141,11 +141,13 @@
 #define CERES_PUBLIC_INTERNAL_AUTODIFF_H_
 
 #include <array>
+#include <cstddef>
 #include <utility>
 
 #include "Eigen/Core"
 #include "absl/log/check.h"
 #include "ceres/internal/array_selector.h"
+#include "ceres/internal/integer_sequence_algorithm.h"
 #include "ceres/internal/variadic_evaluate.h"
 #include "ceres/jet.h"
 #include "ceres/types.h"