diff --git a/tsar-py/Cargo.toml b/tsar-py/Cargo.toml
index 3489169..1900b4a 100644
--- a/tsar-py/Cargo.toml
+++ b/tsar-py/Cargo.toml
@@ -9,6 +9,6 @@ name = "tsar"
 crate-type = ["cdylib"]
 
 [dependencies]
-pyo3 = { version = "0.21.0", features = ["extension-module"] }
+pyo3 = { version = "0.22.0", features = ["extension-module"] }
 rayon = "1.5.3"
 tsar-rs = { path = "../tsar-rs" }
diff --git a/tsar-py/src/lib.rs b/tsar-py/src/lib.rs
index 2144d2e..e235feb 100644
--- a/tsar-py/src/lib.rs
+++ b/tsar-py/src/lib.rs
@@ -32,6 +32,7 @@ impl Writer {
         Ok(())
     }
 
+    #[pyo3(signature = (ty, name, data, dims, error_limit, target_file=None))]
     pub fn write_blob(
         &mut self,
         ty: &str,