--- a/src/google/protobuf/arena.cc	(index)
+++ b/src/google/protobuf/arena.cc	(working tree)
@@ -39,6 +39,7 @@
 #include <typeinfo>
 
 #include "absl/base/attributes.h"
+#include "absl/container/internal/btree.h"
 #include "absl/synchronization/mutex.h"
 #include "google/protobuf/arena_allocation_policy.h"
 #include "google/protobuf/arenaz_sampler.h"