diff --git a/folly/io/async/fdsock/AsyncFdSocket.h b/folly/io/async/fdsock/AsyncFdSocket.h
index d3d84bb5873..8fbfbd9baad 100644
--- a/folly/io/async/fdsock/AsyncFdSocket.h
+++ b/folly/io/async/fdsock/AsyncFdSocket.h
@@ -19,6 +19,16 @@
 #include <folly/io/async/AsyncSocket.h>
 #include <folly/io/async/fdsock/SocketFds.h>
 
+#ifdef __APPLE__
+#include <AvailabilityMacros.h>
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 110000
+#ifdef __DARWIN_ALIGN32
+#undef __DARWIN_ALIGN32
+#define __DARWIN_ALIGN32(p) ((__darwin_size_t)((__darwin_size_t)(p) + __DARWIN_ALIGNBYTES32) &~ __DARWIN_ALIGNBYTES32)
+#endif
+#endif
+#endif
+
 namespace folly {
 
 // Including `gtest/gtest_prod.h` would make gtest/gmock a hard dep