diff --git a/lib/rbs/definition_builder.rb b/lib/rbs/definition_builder.rb
index 715b417a9..13680f031 100644
--- a/lib/rbs/definition_builder.rb
+++ b/lib/rbs/definition_builder.rb
@@ -346,7 +346,7 @@ def build_singleton(type_name)
           if entry.is_a?(Environment::ClassEntry)
             new_method = definition.methods[:new]
 
-            if new_method.defs.all? {|d| d.defined_in == BuiltinNames::Class.name }
+            if new_method && new_method.defs.all? {|d| d.defined_in == BuiltinNames::Class.name }
               # The method is _untyped new_.
 
               alias_methods = definition.methods.each.with_object([]) do |entry, array|