diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b66da21..180ebeb 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,12 +30,6 @@ jobs:
       with:
         submodules: recursive
 
-    - name: Install ancient PHPUnit
-      run: composer require --dev --ignore-platform-reqs phpunit/phpunit "4.8.36"
-
-    - name: Install dependencies
-      run: composer update --no-interaction
-
     - name: Build for PHP 5.5
       env:
         CC: clang
@@ -45,6 +39,13 @@ jobs:
         ./configure
         make
 
+    - name: Install dependencies
+      run: |
+        php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
+        php composer-setup.php
+        php -c php.ini composer.phar require --dev --ignore-platform-reqs phpunit/phpunit "4.8.36"
+        php -c php.ini composer.phar update --no-interaction
+
   php-linux-x64:
     runs-on: ubuntu-latest
     strategy:
@@ -71,9 +72,6 @@ jobs:
       with:
         submodules: recursive
 
-    - name: Install dependencies
-      run: composer update --no-interaction
-
     - name: Run tests
       env:
         CC: clang
@@ -84,6 +82,12 @@ jobs:
         make
         make test
 
+    - name: Install dependencies
+      run: |
+        php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
+        php composer-setup.php
+        php -c php.ini composer.phar update --no-interaction
+
 
   #   linux-arm:
   #     name: ARM (${{ matrix.arch }})
diff --git a/run_tests b/run_tests
index 18b449a..cd19974 100755
--- a/run_tests
+++ b/run_tests
@@ -12,7 +12,8 @@ if [ -z $PHP_BINARY ]; then
 fi
 
 if [ ! -d vendor ]; then
-    composer update
+    COMPOSER_BINARY=$(which composer)
+    $PHP_BINARY -c php.ini $COMPOSER_BINARY update
 fi
 
 $launcher $PHP_BINARY -c php.ini vendor/bin/phpunit tests --debug