diff --git a/Cargo.toml b/Cargo.toml
index 2fd65a0..564de31 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,7 +20,7 @@ name = "tket_json_rs"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 uuid = { version = "1.4", features = ["serde"] }
-pyo3 = { version = "0.20.0", optional = true }
+pyo3 = { version = "0.21.0", optional = true }
 pythonize = { version = "0.20.0", optional = true }