diff --git a/git-compat-util.h b/git-compat-util.h
index 9863cf671f..309240bbce 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -47,9 +47,15 @@
 #include <netdb.h>
 #include <pwd.h>
 #include <inttypes.h>
+#if defined(__CYGWIN__)
+#undef _XOPEN_SOURCE
+#include <grp.h>
+#define _XOPEN_SOURCE 600
+#else
 #undef _ALL_SOURCE /* AIX 5.3L defines a struct list with _ALL_SOURCE. */
 #include <grp.h>
 #define _ALL_SOURCE 1
+#endif
 
 #ifndef NO_ICONV
 #include <iconv.h>