diff --git a/crates/pep440-rs/Cargo.toml b/crates/pep440-rs/Cargo.toml
index d486d309f..076067006 100644
--- a/crates/pep440-rs/Cargo.toml
+++ b/crates/pep440-rs/Cargo.toml
@@ -27,3 +27,7 @@ unscanny = { workspace = true }
 
 [dev-dependencies]
 indoc = { version = "2.0.4" }
+
+[features]
+# Match the API of the published crate, for compatibility.
+serde = []
diff --git a/crates/pep508-rs/Cargo.toml b/crates/pep508-rs/Cargo.toml
index 7e31bdb0b..bb41125af 100644
--- a/crates/pep508-rs/Cargo.toml
+++ b/crates/pep508-rs/Cargo.toml
@@ -52,3 +52,5 @@ tracing = ["dep:tracing", "pep440_rs/tracing"]
 # be supported.
 non-pep508-extensions = []
 default = []
+# Match the API of the published crate, for compatibility.
+serde = []