diff --git a/config2.h.in b/config2.h.in
index b6288e93..0b0bb9b8 100644
--- a/config2.h.in
+++ b/config2.h.in
@@ -919,7 +919,7 @@
 #endif
 /* Enable GNU extensions on systems that have them.  */
 #ifndef _GNU_SOURCE
-# undef _GNU_SOURCE
+# define _GNU_SOURCE
 #endif
 /* Enable threading extensions on Solaris.  */
 #ifndef _POSIX_PTHREAD_SEMANTICS
diff --git a/src/osdep/unix/sysinfo.h b/src/osdep/unix/sysinfo.h
index 55eca3aa..c479e6cf 100644
--- a/src/osdep/unix/sysinfo.h
+++ b/src/osdep/unix/sysinfo.h
@@ -26,6 +26,9 @@ static inline int dir_sep(char x) { return x == '/'; }
 #include <pwd.h>
 #include <grp.h>
 
+#include <unistd.h>
+#include <errno.h>
+
 #endif
 
 #endif