Make php7-zts fails at PEAR installation

[KevinESA]

I'm trying to install this on Debian 9, but I've added the sid and jessie repositories to my apt source.list, so it should be able to download anything. The problem seems to start right where it generates phar.phar:

Generating phar.phar
PEAR package PHP_Archive not installed: generated phar will require PHP's phar exension be enabled.
clicommand.inc
directorygraphiterator.inc
pharcommand.inc
invertedregexiterator.inc
directorytreeiterator.inc
phar.inc

Build complete.
Don't forget to run 'make test'.

Installing shared extensions:     /usr/local/php7-zts/lib/php/extensions/no-debugzts-20160731/
Installing PHP CLI binary:        /usr/local/php7-zts/bin/
Installing PHP CLI man page:      /usr/local/php7-zts/php/man/man1/
Installing phpdbg binary:         /usr/local/php7-zts/bin/
Installing phpdbg man page:       /usr/local/php7-zts/php/man/man1/
Installing build environment:     /usr/local/php7-zts/lib/php/build/
Installing header files:          /usr/local/php7-zts/include/php/
Installing helper programs:       /usr/local/php7-zts/bin/
  program: phpize
  program: php-config
Installing man pages:             /usr/local/php7-zts/php/man/man1/
  page: phpize.1
  page: php-config.1
Installing PEAR environment:      /usr/local/php7-zts/lib/php/
Makefile:439: recipe for target 'install-pear-installer' failed
make[1]: *** [install-pear-installer] Error 255
Makefile:442: recipe for target 'install-pear' failed
make: *** [install-pear] Error 2
Makefile:5: recipe for target 'php7-zts' failed
make: *** [php7-zts] Error 2

I've tried manually installing php7.1 and running the make file again, but I really don't know exactly why it's failing. My research showed that the install command that's it's trying to run may be faulty for some reason or another, but I obviously have no clue where I'd fix that.