diff --git a/3rdparty/udns/udns_rr_a.c b/3rdparty/udns/udns_rr_a.c
index 4fdcbf9b..72cd2022 100644
--- a/3rdparty/udns/udns_rr_a.c
+++ b/3rdparty/udns/udns_rr_a.c
@@ -21,6 +21,9 @@
 
  */
 
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
 #include <string.h>
 #include <stdlib.h>
 #include <assert.h>