diff --git a/lbtt/configure.ac b/lbtt/configure.ac
index f5141caf9..a53650f7f 100644
--- a/lbtt/configure.ac
+++ b/lbtt/configure.ac
@@ -70,6 +70,7 @@ fi
 
 # Check for the availability of headers.
 
+AC_GNU_SOURCE
 AC_HEADER_STDC
 AC_CHECK_HEADERS([libintl.h fcntl.h sys/times.h])
 AC_HEADER_SYS_WAIT
@@ -123,8 +124,6 @@ AC_CHECK_HEADERS(
 
 # Checks for typedefs, structures, and compiler characteristics.
 
-AC_GNU_SOURCE
-
 # Check for the availability of the slist header (an extension to the C++
 # Standard Template Library). (In GCC 3.x the header is in the ext/
 # subdirectory of the directory containing the standard C++ headers.)