diff --git a/ui/src/components/AgentConfigForm.tsx b/ui/src/components/AgentConfigForm.tsx
index 3bb2433c..314ae719 100644
--- a/ui/src/components/AgentConfigForm.tsx
+++ b/ui/src/components/AgentConfigForm.tsx
@@ -518,7 +518,7 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
             </Field>
             <Field label="Capabilities" hint={help.capabilities}>
               <MarkdownEditor
-                value={eff("identity", "capabilities", props.agent.capabilities ?? "")}
+                value={eff("identity", "capabilities", props.agent.capabilities ?? "") ?? ""}
                 onChange={(v) => mark("identity", "capabilities", v || null)}
                 placeholder="Describe what this agent can do..."
                 contentClassName="min-h-[44px] text-sm font-mono"