Parse negative impls
diff --git a/syntax/tokens.rs b/syntax/tokens.rs
index 377fd4c..edbf818 100644
--- a/syntax/tokens.rs
+++ b/syntax/tokens.rs
@@ -148,6 +148,7 @@
 impl ToTokens for Impl {
     fn to_tokens(&self, tokens: &mut TokenStream) {
         self.impl_token.to_tokens(tokens);
+        self.negative_token.to_tokens(tokens);
         self.ty.to_tokens(tokens);
         self.brace_token.surround(tokens, |_tokens| {});
     }