diff --git a/performance.rst b/performance.rst
index 0fb6653b001..5abc2c490bb 100644
--- a/performance.rst
+++ b/performance.rst
@@ -103,6 +103,8 @@ such as Symfony projects, should use at least these values:
     ; save the results for 10 minutes (600 seconds)
     realpath_cache_ttl=600
 
+Note: using ``open_basedir`` will disable the realpath Cache.
+
 .. _performance-optimize-composer-autoloader:
 
 Optimize Composer Autoloader