diff --git a/ReactCommon/cxxreact/JSBigString.h b/ReactCommon/cxxreact/JSBigString.h
index 8711107a0fe..e3cc5af292e 100644
--- a/ReactCommon/cxxreact/JSBigString.h
+++ b/ReactCommon/cxxreact/JSBigString.h
@@ -7,6 +7,7 @@
 
 #include <fcntl.h>
 #include <sys/mman.h>
+#include <unistd.h>
 
 #include <folly/Exception.h>