diff --git a/configure.ac b/configure.ac
index fdf6a8c..a82e721 100644
--- a/configure.ac
+++ b/configure.ac
@@ -21,7 +21,9 @@ AC_HEADER_STDC
 AC_CHECK_HEADERS(fcntl.h limits.h unistd.h)
 AC_CHECK_HEADERS(wordexp.h)
 AC_CHECK_LIB(mswstr, DBLCMapStringW)
-AC_CHECK_DECLS([program_invocation_short_name], [], [], [[#include <errno.h>]])
+AC_CHECK_DECLS([program_invocation_short_name], [], [], [[
+                #define _GNU_SOURCE
+                #include <errno.h>]])
 
 dnl Checks for typedefs, structures, and compiler characteristics.
 AC_C_CONST