Put definition of _REENTRANT in config.h
diff --git a/configure.in b/configure.in
index 226ab68..f74651c 100644
--- a/configure.in
+++ b/configure.in
@@ -247,6 +247,7 @@
 if test -d "$withval"
 then LIBS="$LIBS -L$withval"
 fi
+AC_DEFINE(_REENTRANT)
 AC_CHECK_HEADER(mach/cthreads.h, [AC_DEFINE(WITH_THREAD)
 AC_DEFINE(C_THREADS)
 LIBOBJS="$LIBOBJS thread.o"],[