diff --git a/configure.ac b/configure.ac
index 1c579d2dc..df2d8a5d4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,6 +44,7 @@ AC_CANONICAL_HOST
 AM_PROG_CC_C_O
 AC_USE_SYSTEM_EXTENSIONS
 AC_SYS_LARGEFILE
+AC_GNU_SOURCE
 
 # Test if we have a new enough compiler.
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[