diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 9521feb4..776d4785 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit bootstrap="tests/bootstrap.php">
+<phpunit bootstrap="tests/bootstrap.php"
+         processIsolation="true">
     <testsuites>
         <testsuite name="Monolog Test Suite">
             <directory>tests/Monolog/</directory>