diff --git a/crates/automation/src/signing.rs b/crates/automation/src/signing.rs
index 1a6440fd54..448a2d36d0 100644
--- a/crates/automation/src/signing.rs
+++ b/crates/automation/src/signing.rs
@@ -253,6 +253,11 @@ impl Automation {
         // A dynamic form's signing scripts run only when asked: what preSign changes is signed,
         // and the caller hasn't seen it. What they changed is listed.
         let run_scripts = a.opt_bool("run_form_scripts")?.unwrap_or(false);
+        // Every argument is read before the preSign scripts change anything, so a bad one is
+        // refused with the document as it was.
+        let reason = a.opt_str("reason")?.map(str::to_string);
+        let location = a.opt_str("location")?.map(str::to_string);
+        let contact = a.opt_str("contact")?.map(str::to_string);
         let signing = field.clone();
         let scripted = signing.as_deref().is_some_and(|f| {
             self.session.sign_event_scripted(doc_id, f, SignEvent::Before) || self.session.sign_event_scripted(doc_id, f, SignEvent::After)
@@ -278,19 +283,8 @@ impl Automation {
         } else {
             Vec::new()
         };
-        let opts = SignOptions {
-            field,
-            page,
-            rect,
-            reason: a.opt_str("reason")?.map(str::to_string),
-            location: a.opt_str("location")?.map(str::to_string),
-            contact: a.opt_str("contact")?.map(str::to_string),
-            certify,
-            appearance,
-            appearance_labels,
-            graphic,
-            ..SignOptions::default()
-        };
+        let opts =
+            SignOptions { field, page, rect, reason, location, contact, certify, appearance, appearance_labels, graphic, ..SignOptions::default() };
         let signed = self.session.sign(doc_id, &id, opts).map_err(|e| match e {
             // A graphic the signer refuses is the caller's to fix.
             pdfcraft_engine::EditError::Sign(m) if m.starts_with("the signature graphic") => bad(m),
diff --git a/crates/automation/tests/it/automation.rs b/crates/automation/tests/it/automation.rs
index c50d3d53c2..4e75f6b588 100644
--- a/crates/automation/tests/it/automation.rs
+++ b/crates/automation/tests/it/automation.rs
@@ -5804,6 +5804,21 @@ fn signing_an_xfa_box_runs_its_signing_scripts_through_tools() {
         "{unasked}"
     );
     let doc = ok(&mut a, "doc_open", json!({ "path": "form.pdf" }))["doc"].as_u64().unwrap();
+    // A bad argument is refused before the preSign scripts run.
+    let bad = a.call(
+        "sign_document",
+        &json!({ "doc": doc, "id": "ada.p12", "password": "secret12", "field": name("sign"), "out": "bad.pdf", "run_form_scripts": true, "reason": 5 }),
+    );
+    assert!(matches!(bad, Err(ToolError::InvalidArgs(_))), "{bad:?}");
+    let now = ok(&mut a, "form_fields", json!({ "doc": doc }));
+    assert!(
+        now["fields"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .any(|f| f["name"].as_str().is_some_and(|n| n == "when" || n.ends_with(".when[0]")) && f["value"].is_null()),
+        "{now}"
+    );
     // A signed file that can't be written (`out` is a folder): not signed, and what preSign did
     // is taken back.
     std::fs::create_dir_all(dir.join("taken")).unwrap();