diff --git a/ruma-identifiers-validation/Cargo.toml b/ruma-identifiers-validation/Cargo.toml
index 6f62bb5b..d1109d8e 100644
--- a/ruma-identifiers-validation/Cargo.toml
+++ b/ruma-identifiers-validation/Cargo.toml
@@ -12,5 +12,9 @@ license = "MIT"
 version = "0.1.0"
 edition = "2018"
 
+[features]
+default = ["serde"]
+
 [dependencies]
+serde = { version = "1.0.114", optional = true, features = ["derive"] }
 strum = { version = "0.19.2", features = ["derive"] }