diff --git a/ortools/bop/bop_base.cc b/ortools/bop/bop_base.cc
index 3dfffddb5b..b31ad3d19a 100644
--- a/ortools/bop/bop_base.cc
+++ b/ortools/bop/bop_base.cc
@@ -15,6 +15,7 @@
 
 #include <algorithm>
 #include <cstdint>
+#include <cstdlib>
 #include <limits>
 #include <string>
 #include <vector>
diff --git a/ortools/bop/bop_ls.cc b/ortools/bop/bop_ls.cc
index 33ae64b5c8..39f08c89e2 100644
--- a/ortools/bop/bop_ls.cc
+++ b/ortools/bop/bop_ls.cc
@@ -16,6 +16,7 @@
 #include <algorithm>
 #include <array>
 #include <cstdint>
+#include <cstdlib>
 #include <limits>
 #include <memory>
 #include <string>
diff --git a/ortools/bop/bop_solver.cc b/ortools/bop/bop_solver.cc
index a96a2d7fee..ab0d6d6435 100644
--- a/ortools/bop/bop_solver.cc
+++ b/ortools/bop/bop_solver.cc
@@ -13,6 +13,7 @@
 
 #include "ortools/bop/bop_solver.h"
 
+#include <cstdlib>
 #include <memory>
 #include <string>
 #include <vector>
diff --git a/ortools/bop/integral_solver.cc b/ortools/bop/integral_solver.cc
index 5ef009338e..8813a4d2fd 100644
--- a/ortools/bop/integral_solver.cc
+++ b/ortools/bop/integral_solver.cc
@@ -18,6 +18,7 @@
 #include <algorithm>
 #include <cmath>
 #include <cstdint>
+#include <cstdlib>
 #include <limits>
 #include <memory>
 #include <string>