diff --git a/src/Type/UnionType.php b/src/Type/UnionType.php
index e6bfb30cab..a6ebbcc15c 100644
--- a/src/Type/UnionType.php
+++ b/src/Type/UnionType.php
@@ -19,6 +19,7 @@
 use PHPStan\Reflection\Type\UnresolvedPropertyPrototypeReflection;
 use PHPStan\ShouldNotHappenException;
 use PHPStan\TrinaryLogic;
+use PHPStan\Type\Accessory\AccessoryType;
 use PHPStan\Type\Generic\GenericClassStringType;
 use PHPStan\Type\Generic\TemplateMixedType;
 use PHPStan\Type\Generic\TemplateType;
@@ -67,6 +68,10 @@ public function __construct(private array $types, private bool $normalized = fal
 			$throwException();
 		}
 		foreach ($types as $type) {
+			if ($type instanceof AccessoryType) {
+				// accessory types need to be intersected with a main type
+				$throwException();
+			}
 			if (!($type instanceof UnionType)) {
 				continue;
 			}
diff --git a/tests/PHPStan/Type/UnionTypeTest.php b/tests/PHPStan/Type/UnionTypeTest.php
index cd0ee180cc..4c8a983179 100644
--- a/tests/PHPStan/Type/UnionTypeTest.php
+++ b/tests/PHPStan/Type/UnionTypeTest.php
@@ -8,9 +8,12 @@
 use Iterator;
 use PHPStan\Reflection\Native\NativeParameterReflection;
 use PHPStan\Reflection\PassedByReference;
+use PHPStan\ShouldNotHappenException;
 use PHPStan\Testing\PHPStanTestCase;
 use PHPStan\TrinaryLogic;
 use PHPStan\Type\Accessory\AccessoryLiteralStringType;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
+use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
 use PHPStan\Type\Accessory\AccessoryNumericStringType;
 use PHPStan\Type\Accessory\HasMethodType;
 use PHPStan\Type\Accessory\HasOffsetType;
@@ -1640,4 +1643,30 @@ public function dataGetArrays(): iterable
 		];
 	}
 
+	/**
+	 * @param Type[] $types
+	 *
+	 * @dataProvider dataUnionThrows
+	 */
+	public function testUnionThrows(array $types, string $message): void
+	{
+		$this->expectException(ShouldNotHappenException::class);
+		$this->expectExceptionMessage($message);
+
+		new UnionType($types);
+	}
+
+	public function dataUnionThrows(): array
+	{
+		return [
+			// union type requires at least 2 types
+			[[new AccessoryNonEmptyStringType()], 'Cannot create PHPStan\\Type\\UnionType with: non-empty-string'],
+			// test invalid combinations
+			[[new AccessoryNonFalsyStringType(), new AccessoryNumericStringType()], 'Cannot create PHPStan\\Type\\UnionType with: non-falsy-string, numeric-string'],
+			[[new IntegerType(), new AccessoryNumericStringType()], 'Cannot create PHPStan\\Type\\UnionType with: int, numeric-string'],
+			[[new ArrayType(new IntegerType(), new StringType()), new AccessoryNonEmptyStringType()], 'Cannot create PHPStan\\Type\\UnionType with: array<int, string>, non-empty-string'],
+			[[new IntegerType(), new NonEmptyArrayType()], 'Cannot create PHPStan\\Type\\UnionType with: int, non-empty-array'],
+		];
+	}
+
 }