diff --git a/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php b/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php
index 9b9eb97a6e8..daefaec263d 100644
--- a/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php
+++ b/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php
@@ -1004,6 +1004,9 @@ private static function handleReturn(
                         }
                     }
                 }
+                if (!$new) {
+                    throw new \RuntimeException('Impossible!');
+                }
                 $storage->signature_return_type = new Union($new);
             }