diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index fc53286c..1466f36d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -184,6 +184,7 @@ endif()
 if(WITH_ADNS)
 	cmake_push_check_state()
 	set(ANL_CODE "
+		#define _GNU_SOURCE
 		#include <stdlib.h>
 		#include <netdb.h>
 		int main(){