diff --git a/canvas/src/components/WorkspaceUsage.tsx b/canvas/src/components/WorkspaceUsage.tsx
index 5e51dbc0..9fb1b101 100644
--- a/canvas/src/components/WorkspaceUsage.tsx
+++ b/canvas/src/components/WorkspaceUsage.tsx
@@ -98,7 +98,8 @@ export function WorkspaceUsage({ workspaceId }: WorkspaceUsageProps) {
   );
 }
 
-function formatPeriod(start: string, end: string): string {
+function formatPeriod(start: string | undefined, end: string | undefined): string {
+  if (!start || !end) return "—";
   const fmt = (s: string) =>
     new Date(s).toLocaleDateString(undefined, {
       month: "short",
diff --git a/canvas/src/components/tabs/DetailsTab.tsx b/canvas/src/components/tabs/DetailsTab.tsx
index 9766fc18..5d877cf9 100644
--- a/canvas/src/components/tabs/DetailsTab.tsx
+++ b/canvas/src/components/tabs/DetailsTab.tsx
@@ -189,7 +189,7 @@ export function DetailsTab({ workspaceId, data }: Props) {
             <Row label="Parent" value={data.parentId || "root"} mono />
             <Row label="Active Tasks" value={String(data.activeTasks)} />
             {data.status === "degraded" && (
-              <Row label="Error Rate" value={`${(data.lastErrorRate * 100).toFixed(0)}%`} />
+              <Row label="Error Rate" value={`${((data.lastErrorRate ?? 0) * 100).toFixed(0)}%`} />
             )}
             {isRestartable && (
               <div className="pt-2">