diff --git a/serde_derive/Cargo.toml b/serde_derive/Cargo.toml
index cd3c4b79..8d91a74d 100644
--- a/serde_derive/Cargo.toml
+++ b/serde_derive/Cargo.toml
@@ -5,6 +5,7 @@ authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay
 categories = ["no-std", "no-std::no-alloc"]
 description = "Macros 1.1 implementation of #[derive(Serialize, Deserialize)]"
 documentation = "https://serde.rs/derive.html"
+edition = "2015"
 homepage = "https://serde.rs"
 keywords = ["serde", "serialization", "no_std", "derive"]
 license = "MIT OR Apache-2.0"
diff --git a/serde_derive_internals/Cargo.toml b/serde_derive_internals/Cargo.toml
index 6ce27797..095a7439 100644
--- a/serde_derive_internals/Cargo.toml
+++ b/serde_derive_internals/Cargo.toml
@@ -4,6 +4,7 @@ version = "0.29.0"
 authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
 description = "AST representation used by Serde derive macros. Unstable."
 documentation = "https://docs.rs/serde_derive_internals"
+edition = "2015"
 exclude = ["build.rs"]
 homepage = "https://serde.rs"
 keywords = ["serde", "serialization"]