diff --git a/doc/book/validators/db.md b/doc/book/validators/db.md
index f0434c83c..23d7d21f0 100644
--- a/doc/book/validators/db.md
+++ b/doc/book/validators/db.md
@@ -4,6 +4,16 @@
 a means to test whether a record exists in a given table of a database, with a
 given value.
 
+> ### Installation requirements
+>
+> `Zend\Validator\Db\NoRecordExists` and `Zend\Validator\Db\RecordExists` 
+> depends on the zend-db component, so be sure to have it installed before
+> getting started:
+>
+> ```bash
+> $ composer require zendframework/zend-db`
+> ```
+
 ## Supported options
 
 The following options are supported for `Zend\Validator\Db\NoRecordExists` and
diff --git a/doc/book/validators/digits.md b/doc/book/validators/digits.md
index ee2d7b69f..0792f78ea 100644
--- a/doc/book/validators/digits.md
+++ b/doc/book/validators/digits.md
@@ -2,6 +2,15 @@
 
 `Zend\Validator\Digits` validates if a given value contains only digits.
 
+> ### Installation requirements
+>
+> `Zend\Validator\Digits` depends on the zend-filter component, so be sure to
+> have it installed before getting started:
+>
+> ```bash
+> $ composer require zendframework/zend-filter`
+> ```
+
 ## Supported options
 
 There are no additional options for `Zend\Validator\Digits`:
diff --git a/doc/book/validators/sitemap.md b/doc/book/validators/sitemap.md
index 45228db65..1126febe3 100644
--- a/doc/book/validators/sitemap.md
+++ b/doc/book/validators/sitemap.md
@@ -47,6 +47,15 @@ $validator->isValid('yesterday'); // false
 [Zend\\Uri\\Uri::isValid()](https://zendframework.github.io/zend-uri/usage/#validating-the-uri)
 internally.
 
+> ### Installation requirements
+>
+> `Zend\Validator\Sitemap\Loc` depends on the zend-uri component, so be sure to
+> have it installed before getting started:
+>
+> ```bash
+> $ composer require zendframework/zend-uri`
+> ```
+
 ## Priority
 
 `Zend\Validator\Sitemap\Priority` validates whether a value is valid for using