diff --git a/configure.in b/configure.in
index 2809813..4b3e03d 100644
--- a/configure.in
+++ b/configure.in
@@ -50,6 +50,10 @@
 # them.
 AC_DEFINE(__BSD_VISIBLE, 1, [Define on FreeBSD to activate all library features])
 
+# OpenBSD undoes our definition of __BSD_VISIBLE if _XOPEN_SOURCE is
+# also defined. This can be overridden by defining _BSD_SOURCE
+AC_DEFINE(_BSD_SOURCE, 1, [Define on OpenBSD to activate all library features])
+
 # The later defininition of _XOPEN_SOURCE and _POSIX_C_SOURCE disables
 # u_int on Irix 5.3. Defining _BSD_TYPES brings it back.
 AC_DEFINE(_BSD_TYPES, 1, [Define on Irix to enable u_int])