diff --git a/src/Rules/RuleLevelHelper.php b/src/Rules/RuleLevelHelper.php
index 7fc9724b81..151da55f84 100644
--- a/src/Rules/RuleLevelHelper.php
+++ b/src/Rules/RuleLevelHelper.php
@@ -18,6 +18,7 @@
 use PHPStan\Type\StrictMixedType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
+use PHPStan\Type\TypeTraverser;
 use PHPStan\Type\TypeUtils;
 use PHPStan\Type\UnionType;
 
@@ -60,10 +61,17 @@ public function accepts(Type $acceptingType, Type $acceptedType, bool $strictTyp
 	{
 		if (
 			$this->checkExplicitMixed
-			&& $acceptedType instanceof MixedType
-			&& $acceptedType->isExplicitMixed()
 		) {
-			$acceptedType = new StrictMixedType();
+			$acceptedType = TypeTraverser::map($acceptedType, static function (Type $type, callable $traverse): Type {
+				if (
+					$type instanceof MixedType
+					&& $type->isExplicitMixed()
+				) {
+					return new StrictMixedType();
+				}
+
+				return $traverse($type);
+			});
 		}
 
 		if (
diff --git a/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php b/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php
index cdc7ad1b48..5da2727615 100644
--- a/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php
+++ b/tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php
@@ -11,9 +11,12 @@
 class ReturnTypeRuleTest extends \PHPStan\Testing\RuleTestCase
 {
 
+	/** @var bool */
+	private $checkExplicitMixed = false;
+
 	protected function getRule(): \PHPStan\Rules\Rule
 	{
-		return new ReturnTypeRule(new FunctionReturnTypeCheck(new RuleLevelHelper($this->createReflectionProvider(), true, false, true, false)));
+		return new ReturnTypeRule(new FunctionReturnTypeCheck(new RuleLevelHelper($this->createReflectionProvider(), true, false, true, $this->checkExplicitMixed)));
 	}
 
 	public function testReturnTypeRule(): void
@@ -527,4 +530,15 @@ public function testTemplateUnion(): void
 		]);
 	}
 
+	public function testBug5218(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-5218.php'], [
+			[
+				'Method Bug5218\IA::getIterator() should return Traversable<string, int> but returns ArrayIterator<string, mixed>.',
+				14,
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Methods/data/bug-5218.php b/tests/PHPStan/Rules/Methods/data/bug-5218.php
new file mode 100644
index 0000000000..9388a22e07
--- /dev/null
+++ b/tests/PHPStan/Rules/Methods/data/bug-5218.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace Bug5218;
+
+/**
+ * @phpstan-implements \IteratorAggregate<string, int>
+ */
+final class IA implements \IteratorAggregate
+{
+	/** @var array<string, mixed> */
+	private $data = [];
+
+	public function getIterator() : \Traversable {
+		return new \ArrayIterator($this->data);
+	}
+}