diff --git a/djangorota/djangorota/templates/rota/partials/rota_option_inline.html b/djangorota/djangorota/templates/rota/partials/rota_option_inline.html
index 2afde87..80b8dd5 100644
--- a/djangorota/djangorota/templates/rota/partials/rota_option_inline.html
+++ b/djangorota/djangorota/templates/rota/partials/rota_option_inline.html
@@ -1,6 +1,9 @@
 {% load crispy_forms_tags %}
 <form method="post" hx-post="{{ form_action }}" hx-target="#constraint-row-{{ initial.key|default:"new" }}" hx-swap="outerHTML">
   {% csrf_token %}
+  {% if error %}
+    <div class="notification is-danger">{{ error }}</div>
+  {% endif %}
   <div class="field">
     <label class="label">Key</label>
     <div class="control">
diff --git a/djangorota/rota/views.py b/djangorota/rota/views.py
index ef9bbd2..4a0b0c7 100644
--- a/djangorota/rota/views.py
+++ b/djangorota/rota/views.py
@@ -506,7 +506,18 @@ def rota_option_inline(request, rota_id):
 		val = request.POST.get("value", "")
 		vtype = request.POST.get("type", "string")
 		if not key:
-			return HttpResponseBadRequest("Key is required")
+			# Re-render the inline form with an error message
+			initial = {"key": key, "value": val, "type": vtype}
+			inline_html = render_to_string(
+				"rota/partials/rota_option_inline.html",
+				{"form_action": reverse("rota:rota_option_inline", args=(rota.id,)), "initial": initial, "error": "Key is required", "rota": rota},
+				request=request,
+			)
+			return HttpResponse(inline_html)
+
+		# Try to parse according to type; on failure re-render form with error
+		parsed = None
+		parse_error = None
 		try:
 			if vtype == "int":
 				parsed = int(val)
@@ -519,7 +530,16 @@ def rota_option_inline(request, rota_id):
 			else:
 				parsed = val
 		except Exception as exc:
-			return HttpResponseBadRequest(f"Invalid value: {exc}")
+			parse_error = str(exc)
+
+		if parse_error:
+			initial = {"key": key, "value": val, "type": vtype}
+			inline_html = render_to_string(
+				"rota/partials/rota_option_inline.html",
+				{"form_action": reverse("rota:rota_option_inline", args=(rota.id,)), "initial": initial, "error": f"Invalid value: {parse_error}", "rota": rota},
+				request=request,
+			)
+			return HttpResponse(inline_html)
 
 		opts = rota.options or {}
 		opts[key] = parsed