diff --git a/wait-for b/wait-for
index 5c413d0..4d0553b 100755
--- a/wait-for
+++ b/wait-for
@@ -1,7 +1,7 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
-WAITFOR_TIMEOUT=15
-WAITFOR_QUIET=0
+WAITFOR_TIMEOUT=${WAITFOR_TIMEOUT:-15}
+WAITFOR_QUIET=${WAITFOR_QUIET:-0}
 
 echoerr() {
   if [ "$WAITFOR_QUIET" -ne 1 ]; then printf "%s\n" "$*" 1>&2; fi