diff --git a/lib/danog/PrimeModule.php b/lib/danog/PrimeModule.php
index 789aab8..daba262 100644
--- a/lib/danog/PrimeModule.php
+++ b/lib/danog/PrimeModule.php
@@ -89,10 +89,10 @@ class PrimeModule
     public static function python_single($what)
     {
         if (function_exists('shell_exec')) {
-            $res = trim(shell_exec('timeout 10 python2 '.__DIR__.'/prime.py '.$what.' 2>&1'));
+            $res = trim(shell_exec('timeout 10 python2 '.__DIR__.'/prime.py '.$what.' 2>&1') ?? '');
             if ($res == '' || is_null($res) || !is_numeric($res)) {
                 copy(__DIR__.'/prime.py', getcwd().'/.prime.py');
-                $res = trim(shell_exec('timeout 10 python2 '.getcwd().'/.prime.py '.$what.' 2>&1'));
+                $res = trim(shell_exec('timeout 10 python2 '.getcwd().'/.prime.py '.$what.' 2>&1') ?? '');
                 unlink(getcwd().'/.prime.py');
                 if ($res == '' || is_null($res) || !is_numeric($res)) {
                     return false;
@@ -128,10 +128,10 @@ class PrimeModule
     public static function python_single_alt($what)
     {
         if (function_exists('shell_exec')) {
-            $res = trim(shell_exec('python '.__DIR__.'/alt_prime.py '.$what.' 2>&1'));
+            $res = trim(shell_exec('python '.__DIR__.'/alt_prime.py '.$what.' 2>&1') ?? '');
             if ($res == '' || is_null($res) || !is_numeric($res)) {
                 copy(__DIR__.'/alt_prime.py', getcwd().'/.alt_prime.py');
-                $res = trim(shell_exec('python '.getcwd().'/.alt_prime.py '.$what.' 2>&1'));
+                $res = trim(shell_exec('python '.getcwd().'/.alt_prime.py '.$what.' 2>&1') ?? '');
                 unlink(getcwd().'/.alt_prime.py');
                 if ($res == '' || is_null($res) || !is_numeric($res)) {
                     return false;
diff --git a/tests/install_deps.sh b/tests/install_deps.sh
index 936a566..a9accd7 100755
--- a/tests/install_deps.sh
+++ b/tests/install_deps.sh
@@ -1,17 +1,5 @@
 #!/bin/bash
-export PATH=$PATH:~/.phpenv/versions/$(phpenv version-name)/bin
 
-cd /tmp &&
-git clone https://github.com/CopernicaMarketingSoftware/PHP-CPP &&
-cd PHP-CPP &&
-make -j16 &&
-sudo make install &&
-
-cd ../ &&
-git clone https://github.com/danog/PrimeModule-ext &&
-cd PrimeModule-ext &&
-make -j16 &&
-echo "extension=$PWD/primemodule.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini &&
-cd ..
+sudo apt-get install build-essential && git clone https://github.com/danog/PrimeModule-ext && cd PrimeModule-ext && make -j$(nproc) && sudo make install
 
 exit 0