phpenvのinstallでmcrypt.h not foundが出て進めない

表題の件です。

下記の手順でインストールを行いました。

実行環境

CentOS release 6.5

インストール手順

$ curl -L https://raw.githubusercontent.com/CHH/phpenv/master/bin/phpenv-install.sh | sh
$ export PATH=$HOME/.phpenv/bin:$PATH
$ eval "$(phpenv init -)"
$ source ~/.bashrc

# ここからうまくいかない

$ phpenv install 5.6.10
[Info]: Loaded extension plugin
[Info]: Loaded apc Plugin.
[Info]: Loaded composer Plugin.
[Info]: Loaded pyrus Plugin.
[Info]: Loaded uprofiler Plugin.
[Info]: Loaded xdebug Plugin.
[Info]: Loaded xhprof Plugin.
[Info]: php.ini-production gets used as php.ini
[Info]: Building 5.6.10 into ~/.phpenv/versions/5.6.10
[Skipping]: Already downloaded and extracted http://php.net/distributions/php-5.6.10.tar.bz2
[Preparing]: /tmp/php-build/source/5.6.10

-----------------
|  BUILD ERROR  |
-----------------

Here are the last 10 lines from the log:

-----------------------------------------
configure: error: mcrypt.h not found. Please reinstall libmcrypt.
-----------------------------------------

The full Log is available at '/tmp/php-build.5.6.10.20160707002851.log'.
[Warn]: Aborting build.

libmcryptが見つからない的な事を言ってるのですが、yumでインストール済みでした。

$ sudo yum info libmcrypt
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
 * base: ftp.nara.wide.ad.jp
 * extras: ftp.nara.wide.ad.jp
 * updates: ftp.nara.wide.ad.jp
Installed Packages
Name        : libmcrypt
Arch        : x86_64
Version     : 2.5.8
Release     : 9.el6
Size        : 281 k
Repo        : installed
From repo   : epel
Summary     : Encryption algorithms library
URL         : http://mcrypt.sourceforge.net/
License     : LGPLv2+
Description : Libmcrypt is a thread-safe library providing a uniform interface
            : to access several block and stream encryption algorithm

なぜ phpenv install に失敗してしまうのでしょうか。