diff --git a/configure.ac b/configure.ac
index 813e80e..cccac5b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -55,6 +55,7 @@ AC_HAVE_LIBRARY(mach)
 AC_C_CONST
 AC_TYPE_OFF_T
 AC_TYPE_SIZE_T
+AC_GNU_SOURCE
 # AC_TYPE_SOCKLEN_T
 
 OLD_TYPE_SOCKLEN_T