diff --git a/Cargo.toml b/Cargo.toml
index 39572bf..a90624d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,7 @@ authors = ["David Tolnay <dtolnay@gmail.com>"]
 categories = ["rust-patterns"]
 description = "derive(Error)"
 documentation = "https://docs.rs/thiserror"
-edition = "2018"
+edition = "2021"
 keywords = ["error", "error-handling", "derive"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/thiserror"
diff --git a/impl/Cargo.toml b/impl/Cargo.toml
index affe901..a5bd868 100644
--- a/impl/Cargo.toml
+++ b/impl/Cargo.toml
@@ -3,7 +3,7 @@ name = "thiserror-impl"
 version = "1.0.41"
 authors = ["David Tolnay <dtolnay@gmail.com>"]
 description = "Implementation detail of the `thiserror` crate"
-edition = "2018"
+edition = "2021"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/thiserror"
 rust-version = "1.56"
diff --git a/impl/src/attr.rs b/impl/src/attr.rs
index fe2396f..9af7c60 100644
--- a/impl/src/attr.rs
+++ b/impl/src/attr.rs
@@ -1,7 +1,6 @@
 use proc_macro2::{Delimiter, Group, Span, TokenStream, TokenTree};
 use quote::{format_ident, quote, ToTokens};
 use std::collections::BTreeSet as Set;
-use std::iter::FromIterator;
 use syn::parse::ParseStream;
 use syn::{
     braced, bracketed, parenthesized, token, Attribute, Error, Ident, Index, LitInt, LitStr, Meta,