diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ca3c21c..5577e6a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,7 +19,7 @@ Please also have a look at our
 ### Changed
 
 - Use more native type declarations and strict mode
-  (#641, #772, #774, #778, #804)
+  (#641, #772, #774, #778, #804, #841)
 - Add visibility to all class/interface constants (#469)
 
 ### Deprecated
diff --git a/src/CSSList/CSSList.php b/src/CSSList/CSSList.php
index 9ea81b4c..a747e90c 100644
--- a/src/CSSList/CSSList.php
+++ b/src/CSSList/CSSList.php
@@ -413,7 +413,7 @@ protected function renderListContents(OutputFormat $oOutputFormat)
             $oNextLevel = $oOutputFormat->nextLevel();
         }
         foreach ($this->aContents as $oContent) {
-            $sRendered = $oOutputFormat->safely(function () use ($oNextLevel, $oContent) {
+            $sRendered = $oOutputFormat->safely(static function () use ($oNextLevel, $oContent): string {
                 return $oContent->render($oNextLevel);
             });
             if ($sRendered === null) {
diff --git a/src/RuleSet/RuleSet.php b/src/RuleSet/RuleSet.php
index 62a3d313..8888e9cd 100644
--- a/src/RuleSet/RuleSet.php
+++ b/src/RuleSet/RuleSet.php
@@ -162,7 +162,7 @@ public function getRules($mRule = null)
                 $aResult = \array_merge($aResult, $aRules);
             }
         }
-        \usort($aResult, function (Rule $first, Rule $second) {
+        \usort($aResult, static function (Rule $first, Rule $second): int {
             if ($first->getLineNo() === $second->getLineNo()) {
                 return $first->getColNo() - $second->getColNo();
             }
@@ -266,7 +266,7 @@ protected function renderRules(OutputFormat $oOutputFormat)
         $oNextLevel = $oOutputFormat->nextLevel();
         foreach ($this->aRules as $aRules) {
             foreach ($aRules as $rule) {
-                $sRendered = $oNextLevel->safely(function () use ($rule, $oNextLevel) {
+                $sRendered = $oNextLevel->safely(static function () use ($rule, $oNextLevel): string {
                     return $rule->render($oNextLevel);
                 });
                 if ($sRendered === null) {