--- libX11-1.0.0/configure.ac
+++ libX11-1.0.0/configure.ac
@@ -155,17 +155,19 @@
 AM_CONDITIONAL(THRSTUBS, test x$thrstubs = xyes)
 
 dnl XXX incomplete, please fill this in
-if test x$xthreads = xyes ; then
+[ if test x$xthreads = xyes ; then
     case $host_os in
     linux*|openbsd*)
         XTHREADLIB=-lpthread ;;
     freebsd*)
         XTHREAD_CFLAGS="-D_THREAD_SAFE"
         XTHREADLIB="-pthread" ;;
+    netbsd[3-9]* | netbsdelf[3-9]*)
+        XTHREAD_CFLAGS="-D_REENTRANT -D_POSIX_THREAD_SAFE_FUNCTIONS" ;;
     solaris*)
 	XTHREAD_CFLAGS="-D_REENTRANT -D_POSIX_PTHREAD_SEMANTICS" ;;
     esac
-fi
+fi ]
 AC_SUBST(XTHREADLIB)
 AC_SUBST(XTHREAD_CFLAGS)
 X11_CFLAGS="$X11_CFLAGS $XTHREAD_CFLAGS"