diff --git a/lib/setup.h b/lib/setup.h
index 3ba33dd320..66e7a8670a 100644
--- a/lib/setup.h
+++ b/lib/setup.h
@@ -83,6 +83,7 @@ typedef unsigned char bool;
 #ifdef HAVE_ASSERT_H
 #include <assert.h>
 #endif
+#include <errno.h>
 
 #ifndef OS
 #ifdef WIN32