--- mariadb-10.5.9.old/storage/mroonga/vendor/groonga/lib/error.c
+++ mariadb-10.5.9/storage/mroonga/vendor/groonga/lib/error.c
@@ -16,6 +16,8 @@
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1335  USA
 */
 
+#include <errno.h>
+
 #include "grn_error.h"
 #include "grn_windows.h"