Mac Os X php56-fpm libpng error

I am not very good at library management on mac os x. I am running php56-fpm on mac and am getting the following errors:

dyld: Library not loaded: /usr/local/lib/libpng16.16.dylib
  Referenced from: /usr/local/Cellar/php56/5.6.9/sbin/php-fpm
  Reason: Incompatible library version: php-fpm requires version 34.0.0 or later, but libpng16.16.dylib provides version 29.0.0
/usr/local/opt/php56/sbin/php56-fpm: line 53: 38984 Trace/BPT trap: 5       $php_fpm_BIN --daemonize $php_opts
 failed

      

        
        
        
      

    

Obviously I have the old libpng library installed. I usually uninstall it, find an updated version of the library and install. Unfortunately I don't know how to do this on Mac. I tried uninstalling and reinstalling with brew, but I keep missing outdated libpng. How can I get a new updated version?