diff --git a/src/Type/UnionTypeHelper.php b/src/Type/UnionTypeHelper.php
index bbb097accf..a2c28b3153 100644
--- a/src/Type/UnionTypeHelper.php
+++ b/src/Type/UnionTypeHelper.php
@@ -109,7 +109,10 @@ public static function sortTypes(array $types): array
 				return self::compareStrings($a->describe(VerbosityLevel::value()), $b->describe(VerbosityLevel::value()));
 			}
 
-			if ($a->isCallable()->yes() && $b->isCallable()->yes()) {
+			if (
+				($a instanceof CallableType || $a instanceof ClosureType)
+				&& ($b instanceof CallableType || $b instanceof ClosureType)
+			) {
 				return self::compareStrings($a->describe(VerbosityLevel::value()), $b->describe(VerbosityLevel::value()));
 			}