diff --git a/configure.in b/configure.in
index 3bb8717..cdd1773 100644
--- a/configure.in
+++ b/configure.in
@@ -211,7 +211,7 @@
   # Defining _XOPEN_SOURCE on NetBSD version prior to the introduction of
   # _NETBSD_SOURCE disables certain features (eg. setgroups). Reported by
   # Marc Recht
-  NetBSD/1.5 | NetBSD/1.5.* | NetBSD/1.6 | NetBSD/1.6.* | NetBSD/1.6[A-S])
+  NetBSD/1.5 | NetBSD/1.5.* | NetBSD/1.6 | NetBSD/1.6.* | NetBSD/1.6@<:@A-S@:>@)
     define_xopen_source=no;;
   # On Solaris 2.6, sys/wait.h is inconsistent in the usage
   # of union __?sigval. Reported by Stuart Bishop.