--- configure.bak	2012-05-16 09:40:52.000000000 +0100
+++ configure	2012-05-16 10:02:02.000000000 +0100
@@ -2967,7 +2967,7 @@
 sieveprefixes="/usr /usr/local"
 
 
-$as_echo "#define _GNU_SOURCE ''" >>confdefs.h
+$as_echo '#define _GNU_SOURCE' >>confdefs.h
 
 
 # Turn off both defaults.