diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index 5d87f9c98e..164a9eec03 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -4641,7 +4641,7 @@ private function getTypeToInstantiateForNew(Type $type): Type
 			foreach ($type->getTypes() as $innerType) {
 				$decidedType = $decideType($innerType);
 				if ($decidedType === null) {
-					return new MixedType();
+					return new ObjectWithoutClassType();
 				}
 
 				$types[] = $decidedType;
@@ -4652,7 +4652,7 @@ private function getTypeToInstantiateForNew(Type $type): Type
 
 		$decidedType = $decideType($type);
 		if ($decidedType === null) {
-			return new MixedType();
+			return new ObjectWithoutClassType();
 		}
 
 		return $decidedType;
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index 4a1f5a3082..d168c48d44 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -1712,7 +1712,7 @@ public function dataDeductedTypes(): array
 				'$loremObjectLiteral',
 			],
 			[
-				'mixed',
+				'object',
 				'$mixedObjectLiteral',
 			],
 			[
@@ -10897,6 +10897,11 @@ public function dataBug4577(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4577.php');
 	}
 
+	public function dataBug4579(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4579.php');
+	}
+
 	/**
 	 * @param string $file
 	 * @return array<string, mixed[]>
@@ -11138,6 +11143,7 @@ private function gatherAssertTypes(string $file): array
 	 * @dataProvider dataArrayMapClosure
 	 * @dataProvider dataBug4573
 	 * @dataProvider dataBug4577
+	 * @dataProvider dataBug4579
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args
diff --git a/tests/PHPStan/Analyser/data/bug-4579.php b/tests/PHPStan/Analyser/data/bug-4579.php
new file mode 100644
index 0000000000..5894995591
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/bug-4579.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Bug4579;
+
+use function PHPStan\Analyser\assertType;
+
+function (string $class): void {
+	$foo = new $class();
+	if (method_exists($foo, 'doFoo')) {
+		assertType('object&hasMethod(doFoo)', $foo);
+	}
+};
diff --git a/tests/PHPStan/Analyser/data/generic-class-string.php b/tests/PHPStan/Analyser/data/generic-class-string.php
index 84d74d2d36..2ca7422d1d 100644
--- a/tests/PHPStan/Analyser/data/generic-class-string.php
+++ b/tests/PHPStan/Analyser/data/generic-class-string.php
@@ -15,7 +15,7 @@ public static function f(): int {
  * @param mixed $a
  */
 function testMixed($a) {
-	assertType('mixed', new $a());
+	assertType('object', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('class-string<DateTimeInterface>|DateTimeInterface', $a);
@@ -36,7 +36,7 @@ function testMixed($a) {
  * @param object $a
  */
 function testObject($a) {
-	assertType('mixed', new $a());
+	assertType('object', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('DateTimeInterface', $a);
@@ -47,7 +47,7 @@ function testObject($a) {
  * @param string $a
  */
 function testString($a) {
-	assertType('mixed', new $a());
+	assertType('object', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('class-string<DateTimeInterface>', $a);
@@ -63,7 +63,7 @@ function testString($a) {
  * @param string|object $a
  */
 function testStringObject($a) {
-	assertType('mixed', new $a());
+	assertType('object', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('class-string<DateTimeInterface>|DateTimeInterface', $a);
@@ -92,6 +92,7 @@ function testClassExists(string $str)
 	assertType('string', $str);
 	if (class_exists($str)) {
 		assertType('class-string', $str);
+		assertType('object', new $str());
 	}
 
 	$existentClass = \stdClass::class;