diff --git a/source/posix/cross_process_lock.c b/source/posix/cross_process_lock.c
index e88b4bb2a..1e6db0bbb 100644
--- a/source/posix/cross_process_lock.c
+++ b/source/posix/cross_process_lock.c
@@ -6,6 +6,7 @@
 
 #include <aws/common/byte_buf.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <sys/file.h>
 #include <unistd.h>