diff --git a/src/Action/CreateFinalConfigurationData.php b/src/Action/CreateFinalConfigurationData.php
index 0fa84cd..2d33f96 100644
--- a/src/Action/CreateFinalConfigurationData.php
+++ b/src/Action/CreateFinalConfigurationData.php
@@ -39,7 +39,8 @@ final class CreateFinalConfigurationData
         ];
 
         $configurationData['dockerfile']['stages']['build']['packages'] = $basePackages;
-        $configurationData['dockerfile']['stages']['build']['extensions'] = $phpExtensions;
+
+        $configurationData['dockerfile']['stages']['build']['extensions']['install'] = $phpExtensions;
 
         return $next($configurationData);
     }