diff --git a/posix/fd.cpp b/posix/fd.cpp
index 64a226b4..a0229fd7 100644
--- a/posix/fd.cpp
+++ b/posix/fd.cpp
@@ -15,6 +15,10 @@
 #include <fcntl.h>
 #include <unistd.h>
 
+#if !defined(O_BINARY)
+#define O_BINARY 0
+#endif
+
 using cruft::posix::fd;