diff --git a/lib/Support/raw_ostream.cpp b/lib/Support/raw_ostream.cpp
index f3bcfa1b14a..dceccad161d 100644
--- a/lib/Support/raw_ostream.cpp
+++ b/lib/Support/raw_ostream.cpp
@@ -32,6 +32,10 @@
 # include <fcntl.h>
 #endif
 
+#if defined(__CYGWIN__)
+#include <io.h>
+#endif
+
 #if defined(_MSC_VER)
 #include <io.h>
 #include <fcntl.h>