diff --git a/validation.rst b/validation.rst
index ae73527188c..b8a5276c4e4 100644
--- a/validation.rst
+++ b/validation.rst
@@ -611,6 +611,13 @@ class to have at least 3 characters.
             }
         }
 
+.. caution::
+
+    With PHP 7.4, typed properties were introduced. If a property is accessed
+    before a value is assigned (explicitly or as a default value), PHP will
+    throw an exception. To avoid that, the Validator will use ``null`` as the
+    properties value if it's uninitialized.
+
 .. index::
    single: Validation; Getter constraints