Index: configure.ac
--- configure.ac.orig
+++ configure.ac
@@ -658,6 +658,11 @@ case $host in
     #AC_SUBST(OS_MACOS)
     ;;
 
+    *-openbsd*)
+    AC_MSG_RESULT([OpenBSD])
+    ADDITIONAL_CFLAGS="-D_GNU_SOURCE -DWITH_POSIX"
+    ;;
+
     *-freebsd1*)
     AC_MSG_RESULT([FreeBSD-1x])
     ADDITIONAL_CFLAGS="-D_GNU_SOURCE"