diff --git a/support/xhpast/find_flex.sh b/support/xhpast/find_flex.sh
index c3ea660..6ec43c1 100755
--- a/support/xhpast/find_flex.sh
+++ b/support/xhpast/find_flex.sh
@@ -1,25 +1,25 @@
-#!/bin/sh
+#!/bin/bash
 
 FLEX=`which flex35 2>/dev/null || which flex 2>/dev/null`
 if [ $? -ne 0 ]
 then
   echo "ERROR: 'flex' is not installed on this system." 1>&2;
   exit 1;
 fi
 
 FLEXVERSION=`"$FLEX" --version`
 
 if [[ $FLEXVERSION == "flex 2.5.4" ]]
 then
   echo "ERROR: the version of flex on this system is too old." 1>&2
   echo "Upgrade to at least 2.5.35 (which is NEWER than 2.5.4)." 1>&2
   exit 1;
 fi
 
 if [ "$FLEXVERSION" != "flex 2.5.35" -a "$FLEXVERSION" != "flex35 2.5.35" ]
 then
   echo "WARNING: the version of flex on this system may be incorrect." 1>&2
   echo "If you receive errors, try upgrading to 2.5.35 or newer." 1>&2
 fi
 
 echo $FLEX