diff --git a/src-tauri/src/commands/license_commands.rs b/src-tauri/src/commands/license_commands.rs
index 67cb668..051d5ca 100644
--- a/src-tauri/src/commands/license_commands.rs
+++ b/src-tauri/src/commands/license_commands.rs
@@ -469,14 +469,10 @@ async fn post_license_api(
     }
 }
 
-/// Activation call, without `AppHandle` nor disk access so tests can point it at a mock
-/// server. Returns the activation token issued for `machine_id`.
-async fn activate_inner(
-    api_base: &str,
-    license_key: &str,
-    machine_id: &str,
-    machine_name: Option<&str>,
-) -> Result<String, LicenseError> {
+/// Body of an activation request. `machine_name` is omitted, never sent as `null`, when
+/// the host name is unreadable: the server's schema (`z.string().optional()`) answers
+/// `400 invalid_input` to a null.
+fn activate_body(license_key: &str, machine_id: &str, machine_name: Option<&str>) -> serde_json::Value {
     let mut body = serde_json::json!({
         "product": PRODUCT,
         "license_key": license_key.trim(),
@@ -485,6 +481,18 @@ async fn activate_inner(
     if let Some(name) = machine_name {
         body["machine_name"] = serde_json::Value::String(name.to_string());
     }
+    body
+}
+
+/// Activation call, without `AppHandle` nor disk access so tests can point it at a mock
+/// server. Returns the activation token issued for `machine_id`.
+async fn activate_inner(
+    api_base: &str,
+    license_key: &str,
+    machine_id: &str,
+    machine_name: Option<&str>,
+) -> Result<String, LicenseError> {
+    let body = activate_body(license_key, machine_id, machine_name);
     let resp = post_license_api(api_base, "/v1/licenses/activate", &body).await?;
     resp["activation_token"]
         .as_str()
@@ -1115,6 +1123,35 @@ mod license_server_tests {
         );
     }
 
+    #[test]
+    fn activate_body_omits_an_unknown_machine_name() {
+        let body = activate_body("SR-BASE-k", "machine-1", None);
+        assert!(body.get("machine_name").is_none(), "body {}", body);
+        assert_eq!(body["product"], "simpl-resultat");
+        assert_eq!(
+            activate_body("SR-BASE-k", "machine-1", Some("laptop"))["machine_name"],
+            "laptop"
+        );
+    }
+
+    #[tokio::test]
+    async fn deactivate_with_an_unreadable_success_body_is_an_invalid_response() {
+        // A 2xx the client cannot read proves nothing: counting it as a success would
+        // make the command delete this machine's local token for nothing.
+        let mut server = mockito::Server::new_async().await;
+        let _m = server
+            .mock("POST", "/v1/licenses/deactivate")
+            .with_status(200)
+            .with_header("content-type", "text/html")
+            .with_body("<html>OK</html>")
+            .create_async()
+            .await;
+        assert_eq!(
+            deactivate_inner(&server.url(), "SR-BASE-k", "machine-2").await,
+            Err(LicenseError::InvalidResponse)
+        );
+    }
+
     #[tokio::test]
     async fn activate_posts_the_trimmed_key_and_product_to_v1() {
         let mut server = mockito::Server::new_async().await;
diff --git a/src/hooks/useLicenseMachines.test.ts b/src/hooks/useLicenseMachines.test.ts
index 47f53a9..1afbd06 100644
--- a/src/hooks/useLicenseMachines.test.ts
+++ b/src/hooks/useLicenseMachines.test.ts
@@ -230,6 +230,20 @@ describe("selectCanActivate", () => {
     expect(selectCanActivate(reduce([{ type: "ACTIVATE_START" }]))).toBe(false);
   });
 
+  it("blocks the button while a deactivation is running", () => {
+    // An activation racing the deactivation after a 409 could reach the server
+    // first: the machine-limit message would vanish with 5 calls already spent.
+    const s = reduce(
+      [
+        { type: "LIST_LOAD_START" },
+        { type: "LIST_LOAD_DONE", machines: [machine("a"), machine("b")] },
+        { type: "DEACTIVATE_START", machineId: "a" },
+      ],
+      limitHit,
+    );
+    expect(selectCanActivate(s)).toBe(false);
+  });
+
   it("blocks the button while the list loads", () => {
     // Otherwise a verify answer landing after a successful activation would
     // mark as fresh a list that no longer includes this machine.
diff --git a/src/hooks/useLicenseMachines.ts b/src/hooks/useLicenseMachines.ts
index 6e33991..e90b817 100644
--- a/src/hooks/useLicenseMachines.ts
+++ b/src/hooks/useLicenseMachines.ts
@@ -136,12 +136,13 @@ export function selectCanDeactivate(state: LicenseMachinesState): boolean {
 }
 
 /**
- * The Activate button is live only when no activation and no list reload is running.
- * Same reason as for deactivation: a verify answer landing after a successful
- * activation would mark as fresh a list that no longer includes this machine.
+ * The Activate button is live only when no activation, no list reload and no
+ * deactivation is running. A verify answer landing after a successful activation would
+ * mark as fresh a list that no longer includes this machine; an activation racing a
+ * deactivation could clear the machine-limit message and spend the rate budget.
  */
 export function selectCanActivate(state: LicenseMachinesState): boolean {
-  return !state.activating && !state.listLoading;
+  return !state.activating && !state.listLoading && state.deactivatingId === null;
 }
 
 /** Whether opening the list (from `state`, before the toggle) should load it. */