diff --git a/src/unix/cygwin.c b/src/unix/cygwin.c
index 024e7d5b..25ff02c9 100644
--- a/src/unix/cygwin.c
+++ b/src/unix/cygwin.c
@@ -24,6 +24,7 @@
 #include <stdint.h>
 #include <stddef.h>
 #include <errno.h>
+#include <unistd.h>
 #include <time.h>
 
 #undef NANOSEC