diff --git a/nextnumber b/nextnumber
index ab411ac..6b91a92 100755
--- a/nextnumber
+++ b/nextnumber
@@ -1,7 +1,10 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # TODO: Find a less trashy way to get the next available error code
-
-shopt -s globstar
+if ! shopt -s globstar
+then
+  echo "Error: This script depends on Bash 4." >&2
+  exit 1
+fi
 
 for i in 1 2
 do