diff --git a/CHANGELOG.md b/CHANGELOG.md
index cab8e1e9..7c4d653b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Passing a `string` or `null` to `RuleSet::removeRule()` is deprecated
   (implementing classes are `AtRuleSet` and `DeclarationBlock`);
   use `removeMatchingRules()` or `removeAllRules()` instead (#1249)
+- Passing a `Rule` to `RuleSet::getRules()` or `getRulesAssoc()` is deprecated,
+  affecting the implementing classes `AtRuleSet` and `DeclarationBlock`
+  (call e.g. `getRules($rule->getRule())` instead) (#1248)
 - Passing a string as the first argument to `getAllValues()` is deprecated;
   the search pattern should now be passed as the second argument (#1241)
 - Passing a Boolean as the second argument to `getAllValues()` is deprecated;
diff --git a/src/RuleSet/RuleSet.php b/src/RuleSet/RuleSet.php
index 8cd4904d..1658154c 100644
--- a/src/RuleSet/RuleSet.php
+++ b/src/RuleSet/RuleSet.php
@@ -146,7 +146,8 @@ public function addRule(Rule $oRule, $oSibling = null)
      *        Pattern to search for. If null, returns all rules.
      *        If the pattern ends with a dash, all rules starting with the pattern are returned
      *        as well as one matching the pattern with the dash excluded.
-     *        Passing a Rule behaves like calling `getRules($mRule->getRule())`.
+     *        Passing a `Rule` for this parameter is deprecated in version 8.9.0, and will not work from v9.0.
+     *        Call `getRules($rule->getRule())` instead.
      *
      * @return array<int, Rule>
      */
@@ -205,7 +206,9 @@ public function setRules(array $aRules)
      * @param Rule|string|null $mRule $mRule
      *        Pattern to search for. If null, returns all rules. If the pattern ends with a dash,
      *        all rules starting with the pattern are returned as well as one matching the pattern with the dash
-     *        excluded. Passing a Rule behaves like calling `getRules($mRule->getRule())`.
+     *        excluded.
+     *        Passing a `Rule` for this parameter is deprecated in version 8.9.0, and will not work from v9.0.
+     *        Call `getRulesAssoc($rule->getRule())` instead.
      *
      * @return array<string, Rule>
      */