diff --git a/build/code_sniffer/ruleset-php-strict.xml b/build/code_sniffer/ruleset-php-strict.xml
index 9e01d0c7b9..5e3c26a616 100644
--- a/build/code_sniffer/ruleset-php-strict.xml
+++ b/build/code_sniffer/ruleset-php-strict.xml
@@ -40,6 +40,9 @@
  <!-- A file MUST not contain more than one class/interface -->
  <rule ref="PSR1.Classes.ClassDeclaration.MultipleClasses" />
 
+ <!-- Files containing classes MUST not have any side-effects -->
+ <rule ref="PSR1.Files.SideEffects.FoundWithSymbols" />
+
  <!-- When present, all use declarations MUST go after the namespace declaration.
       There MUST be one use keyword per declaration.
       There MUST be one blank line after the use block. -->