diff --git a/app/routes/api.py b/app/routes/api.py
index 64b127a7..b34ea85f 100644
--- a/app/routes/api.py
+++ b/app/routes/api.py
@@ -6,6 +6,7 @@
 import uuid
 
 from fastapi import APIRouter, Depends, HTTPException, Request, status
+from pydantic import ValidationError
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import selectinload
 from sqlmodel import Session, select
@@ -14,7 +15,7 @@
 from app.models.user import PublicContact, UserModel, user_update_instance
 from app.util.auth_dependencies import CurrentMember
 from app.util.database import get_session
-from app.util.forms import FORM_CORRECT_ANSWERS, Forms, apply_fuzzy_parsing, iter_form_elements, transform_dict, wrong_quiz_answers
+from app.util.forms import FORM_CORRECT_ANSWERS, Forms, apply_fuzzy_parsing, form_field_labels, iter_form_elements, transform_dict, wrong_quiz_answers
 from app.util.kennelish import Transformer
 
 logger = logging.getLogger(__name__)
@@ -177,7 +178,20 @@ async def post_form(
     except json.JSONDecodeError:
         return {"description": "Malformed JSON input."}
 
-    model_validated = model(**inp).model_dump()
+    try:
+        model_validated = model(**inp).model_dump()
+    except ValidationError as e:
+        # A typo'd email, or a radio answer from a page opened before the
+        # form's options changed. That's the member's to fix, not a crash;
+        # log field names and error types only, since the input is PII.
+        failures = [(str(err["loc"][0]) if err["loc"] else "", err["type"]) for err in e.errors()]
+        logger.warning("Form %s submit failed validation: %s", num, failures)
+        bad_keys = list(dict.fromkeys(key for key, _ in failures))
+        labels = form_field_labels(kennelish_data)
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail="Please check: " + "; ".join(labels.get(key, key) for key in bad_keys) + ". If the form changed since you opened it, reload the page and try again.",
+        ) from e
 
     # Grade quiz-style radios, if this form has any. Wrong answers bounce
     # the submission back instead of getting silently recorded.
diff --git a/app/util/forms.py b/app/util/forms.py
index ce9fad1a..8eecbbd7 100644
--- a/app/util/forms.py
+++ b/app/util/forms.py
@@ -59,6 +59,23 @@ def iter_form_elements(kennelish_data):
             yield from iter_form_elements(el.get("elements"))
 
 
+def form_field_labels(kennelish_data) -> dict[str, str]:
+    """
+    Map each field key in a Kennelish form to what the member sees it called:
+    its label, else the nearest h3 above it (quiz radios only carry a generic
+    "What do you do?" caption), else its caption, else the key itself.
+    """
+    labels = {}
+    heading = None
+    for el in iter_form_elements(kennelish_data):
+        if el.get("input") == "h3":
+            heading = el.get("label")
+        key = el.get("key")
+        if key:
+            labels[key] = el.get("label") or heading or el.get("caption") or key
+    return labels
+
+
 def wrong_quiz_answers(num: str, kennelish_data, submitted: dict) -> list[str]:
     """
     Return the headings of the quiz questions in form `num` that `submitted`
diff --git a/tests/test_admin_compliance.py b/tests/test_admin_compliance.py
index 7beb21ab..2f148142 100644
--- a/tests/test_admin_compliance.py
+++ b/tests/test_admin_compliance.py
@@ -53,6 +53,21 @@ def test_wrong_answer_names_the_question(client: TestClient, session: Session, a
     assert not admin_user.admin_compliance_signtime
 
 
+def test_stale_option_is_a_friendly_422(client: TestClient, untrained_admin_jwt: str):
+    # Page opened before an option's wording changed, submitted after.
+    body = {**ANSWERS, "admin_compliance_reporter_ack": "Ask for members consent before sending their emails"}
+    response = client.post(f"/api/form/{FORM}", cookies={"token": untrained_admin_jwt}, json=body)
+    assert response.status_code == 422
+    assert "Scenario 1" in response.json()["detail"]
+    assert "reload the page" in response.json()["detail"]
+
+
+def test_malformed_email_is_a_friendly_422(client: TestClient, jwt: str):
+    response = client.post("/api/form/2", cookies={"token": jwt}, json={"email": "someone@nodomain"})
+    assert response.status_code == 422
+    assert "Preferred Email" in response.json()["detail"]
+
+
 def test_passing_unlocks_panel_and_stamps_signtime_server_side(client: TestClient, session: Session, admin_user: UserModel, untrained_admin_jwt: str):
     # No signature time in the body: the server sets it on a pass.
     response = client.post(f"/api/form/{FORM}", cookies={"token": untrained_admin_jwt}, json=ANSWERS)