diff --git a/src/circuit_json.rs b/src/circuit_json.rs
index 74111a4..566cf96 100644
--- a/src/circuit_json.rs
+++ b/src/circuit_json.rs
@@ -137,6 +137,17 @@ pub enum Classical {
     },
 }
 
+/// Additional fields for Wasm operations.
+#[derive(Deserialize, Serialize, Clone, Debug, PartialEq)]
+pub struct Wasm {
+    n: u64,
+    ww_n: u64,
+    width_i_parameter: Vec<u64>,
+    width_o_parameter: Vec<u64>,
+    func_name: String,
+    wasm_file_uid: String,
+}
+
 /// Serializable operation descriptor.
 #[derive(Deserialize, Serialize, Clone, Debug, PartialEq)]
 #[non_exhaustive]
@@ -166,6 +177,9 @@ pub struct Operation<P = String> {
     /// Data for commands which only act on Bits classically.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub classical: Option<Box<Classical>>,
+    /// Data for commands which apply WASM operations.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub wasm: Option<Box<Wasm>>,
 }
 
 /// Operation applied in a circuit, with defined arguments.
@@ -206,6 +220,9 @@ pub struct SerialCircuit<P = String> {
     pub bits: Vec<Register>,
     /// Implicit permutation of the output qubits.
     pub implicit_permutation: Vec<ImplicitPermutation>,
+    /// Number of wasm wires in the circuit.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub number_of_ws: Option<u64>,
 }
 
 impl<P> Default for Operation<P> {
@@ -219,6 +236,7 @@ impl<P> Default for Operation<P> {
             signature: None,
             conditional: None,
             classical: None,
+            wasm: None,
         }
     }
 }
diff --git a/tests/data/wasm.json b/tests/data/wasm.json
new file mode 100644
index 0000000..ff1cef5
--- /dev/null
+++ b/tests/data/wasm.json
@@ -0,0 +1,35 @@
+{
+  "bits": [],
+  "commands": [
+    {
+      "args": [["_w", [0]]],
+      "op": {
+        "type": "WASM",
+        "wasm": {
+          "func_name": "add_two",
+          "n": 0,
+          "wasm_file_uid": "6a0a29e235cd5c60353254bc2b459e631d381cdd0bded7ae6cb44afb784bd2de",
+          "width_i_parameter": [0],
+          "width_o_parameter": [0],
+          "ww_n": 1
+        }
+      }
+    }
+  ],
+  "implicit_permutation": [
+    [
+      ["q", [0]],
+      ["q", [0]]
+    ],
+    [
+      ["q", [1]],
+      ["q", [1]]
+    ]
+  ],
+  "number_of_ws": 1,
+  "phase": "0.0",
+  "qubits": [
+    ["q", [0]],
+    ["q", [1]]
+  ]
+}
diff --git a/tests/roundtrip.rs b/tests/roundtrip.rs
index e3c1466..41aa4ea 100644
--- a/tests/roundtrip.rs
+++ b/tests/roundtrip.rs
@@ -7,11 +7,13 @@ use tket_json_rs::SerialCircuit;
 const SIMPLE: &str = include_str!("data/simple.json");
 const CLASSICAL: &str = include_str!("data/classical.json");
 const DIAGONAL: &str = include_str!("data/diagonal-box.json");
+const WASM: &str = include_str!("data/wasm.json");
 
 #[rstest]
 #[case::simple(SIMPLE, 4)]
 #[case::classical(CLASSICAL, 3)]
 #[case::diagonal_box(DIAGONAL, 1)]
+#[case::wasm_box(WASM, 1)]
 fn roundtrip(#[case] json: &str, #[case] num_commands: usize) {
     let initial_json: Value = serde_json::from_str(json).unwrap();
     let ser: SerialCircuit = serde_json::from_value(initial_json.clone()).unwrap();