diff --git a/.github/workflows/behat.yml b/.github/workflows/behat.yml
index 0d608b2..bb7efe1 100644
--- a/.github/workflows/behat.yml
+++ b/.github/workflows/behat.yml
@@ -25,4 +25,6 @@ jobs:
         run: composer install
 
       - name: Run behat
-        run: vendor/bin/behat
+        run: |
+          BEHAT_RUN_AS=$(ls -ld behat.yml | awk '{print $3}')
+          vendor/bin/behat
diff --git a/behat.yml b/behat.yml
index 8c62775..ec55888 100644
--- a/behat.yml
+++ b/behat.yml
@@ -1,3 +1,4 @@
 default:
   extensions:
-      PhpBuiltin\Server: ~
+      PhpBuiltin\Server:
+        runAs: www-data
diff --git a/src/RunServerListener.php b/src/RunServerListener.php
index 2972e2b..d4c303b 100644
--- a/src/RunServerListener.php
+++ b/src/RunServerListener.php
@@ -114,7 +114,10 @@ public function start(): void
         }
 
         if (!$this->isRunning()) {
-            throw new ServerException('Failed to start server. Is something already running on port ' . self::$port . '?');
+            throw new ServerException(
+                'Failed to start server. Is something already running on port ' . self::$port . "?\n" .
+                'Full command: ' . $fullCmd
+            );
         }
 
         register_shutdown_function(function () {
@@ -162,7 +165,7 @@ public function killZombies(): void
             'grep "php -S ' . self::$host . '"|' .
             'grep -v grep|' .
             'sed -e "s/^[[:space:]]*//"|cut -d" " -f1';
-        $pids = trim(exec($cmd));
+        $pids = trim(shell_exec($cmd));
         $pids = explode("\n", $pids);
         foreach ($pids as $pid) {
             if ($pid) {
diff --git a/tests/psalm-baseline.xml b/tests/psalm-baseline.xml
index 4e198d3..44c9394 100644
--- a/tests/psalm-baseline.xml
+++ b/tests/psalm-baseline.xml
@@ -1,8 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<files psalm-version="5.12.0@f90118cdeacd0088e7215e64c0c99ceca819e176">
-  <file src="src/Server.php">
-    <UndefinedInterfaceMethod>
-      <code>scalarNode</code>
-    </UndefinedInterfaceMethod>
+<files psalm-version="5.4.0@62db5d4f6a7ae0a20f7cc5a4952d730272fc0863">
+  <file src="src/RunServerListener.php">
+    <ForbiddenCode occurrences="1">
+      <code>shell_exec($cmd)</code>
+    </ForbiddenCode>
+    <PossiblyNullArgument occurrences="1">
+      <code>shell_exec($cmd)</code>
+    </PossiblyNullArgument>
   </file>
 </files>