diff --git a/site/src/pages/TaskPage/TaskApps.tsx b/site/src/pages/TaskPage/TaskApps.tsx
index 26d8562d1e..7921a493e0 100644
--- a/site/src/pages/TaskPage/TaskApps.tsx
+++ b/site/src/pages/TaskPage/TaskApps.tsx
@@ -9,6 +9,7 @@ import {
 import { ExternalImage } from "components/ExternalImage/ExternalImage";
 import { InfoTooltip } from "components/InfoTooltip/InfoTooltip";
 import { Link } from "components/Link/Link";
+import { useProxy } from "contexts/ProxyContext";
 import { ChevronDownIcon, LayoutGridIcon } from "lucide-react";
 import { useAppLink } from "modules/apps/useAppLink";
 import type { Task } from "modules/tasks/tasks";
@@ -18,6 +19,7 @@ import { Link as RouterLink } from "react-router";
 import { cn } from "utils/cn";
 import { docs } from "utils/docs";
 import { TaskAppIFrame } from "./TaskAppIframe";
+import { TaskWildcardWarning } from "./TaskWildcardWarning";
 
 type TaskAppsProps = {
 	task: Task;
@@ -29,6 +31,8 @@ type AppWithAgent = {
 };
 
 export const TaskApps: FC<TaskAppsProps> = ({ task }) => {
+	const { proxy } = useProxy();
+
 	const agents = task.workspace.latest_build.resources
 		.flatMap((r) => r.agents)
 		.filter((a) => !!a);
@@ -54,6 +58,10 @@ export const TaskApps: FC<TaskAppsProps> = ({ task }) => {
 		embeddedApps[0]?.app.id,
 	);
 
+	const activeApp = embeddedApps.find(({ app }) => app.id === activeAppId)?.app;
+	const shouldDisplayWildcardWarning =
+		activeApp?.subdomain && !proxy.proxy?.wildcard_hostname;
+
 	return (
 		<main className="flex flex-col">
 			<div className="w-full flex items-center border-0 border-b border-border border-solid">
@@ -83,18 +91,22 @@ export const TaskApps: FC<TaskAppsProps> = ({ task }) => {
 			</div>
 
 			{embeddedApps.length > 0 ? (
-				<div className="flex-1">
-					{embeddedApps.map(({ app }) => {
-						return (
+				shouldDisplayWildcardWarning ? (
+					<div className="flex-1 flex flex-col items-center justify-center pb-4">
+						<TaskWildcardWarning className="max-w-xl" />
+					</div>
+				) : (
+					<div className="flex-1">
+						{embeddedApps.map(({ app }) => (
 							<TaskAppIFrame
 								key={app.id}
 								active={activeAppId === app.id}
 								app={app}
 								task={task}
 							/>
-						);
-					})}
-				</div>
+						))}
+					</div>
+				)
 			) : (
 				<div className="mx-auto my-auto flex flex-col items-center">
 					<h3 className="font-medium text-content-primary text-base">
diff --git a/site/src/pages/TaskPage/TaskSidebar.tsx b/site/src/pages/TaskPage/TaskSidebar.tsx
index eb1aeb6d59..5e863e375b 100644
--- a/site/src/pages/TaskPage/TaskSidebar.tsx
+++ b/site/src/pages/TaskPage/TaskSidebar.tsx
@@ -1,8 +1,10 @@
 import type { WorkspaceApp } from "api/typesGenerated";
 import { Spinner } from "components/Spinner/Spinner";
+import { useProxy } from "contexts/ProxyContext";
 import type { Task } from "modules/tasks/tasks";
 import type { FC } from "react";
 import { TaskAppIFrame } from "./TaskAppIframe";
+import { TaskWildcardWarning } from "./TaskWildcardWarning";
 
 type TaskSidebarProps = {
 	task: Task;
@@ -64,21 +66,29 @@ const getSidebarApp = (task: Task): [WorkspaceApp | null, SidebarAppStatus] => {
 };
 
 export const TaskSidebar: FC<TaskSidebarProps> = ({ task }) => {
+	const proxy = useProxy();
+
 	const [sidebarApp, sidebarAppStatus] = getSidebarApp(task);
+	const shouldDisplayWildcardWarning =
+		sidebarApp?.subdomain && proxy.proxy?.preferredWildcardHostname === "";
 
 	return (
 		<aside className="flex flex-col h-full shrink-0 w-full">
-			{sidebarAppStatus === "healthy" && sidebarApp ? (
+			{sidebarAppStatus === "loading" ? (
+				<div className="flex-1 flex flex-col items-center justify-center pb-4">
+					<Spinner loading />
+				</div>
+			) : shouldDisplayWildcardWarning ? (
+				<div className="flex-1 flex flex-col items-center justify-center pb-4">
+					<TaskWildcardWarning className="max-w-xl" />
+				</div>
+			) : sidebarAppStatus === "healthy" && sidebarApp ? (
 				<TaskAppIFrame
 					active
 					key={sidebarApp.id}
 					app={sidebarApp}
 					task={task}
 				/>
-			) : sidebarAppStatus === "loading" ? (
-				<div className="flex-1 flex flex-col items-center justify-center">
-					<Spinner loading className="mb-4" />
-				</div>
 			) : (
 				<div className="flex-1 flex flex-col items-center justify-center">
 					<h3 className="m-0 font-medium text-content-primary text-base">
diff --git a/site/src/pages/TaskPage/TaskWildcardWarning.tsx b/site/src/pages/TaskPage/TaskWildcardWarning.tsx
new file mode 100644
index 0000000000..b28e8167a5
--- /dev/null
+++ b/site/src/pages/TaskPage/TaskWildcardWarning.tsx
@@ -0,0 +1,49 @@
+import { Button } from "components/Button/Button";
+import { useAuthenticated } from "hooks/useAuthenticated";
+import { SquareArrowOutUpRightIcon } from "lucide-react";
+import { Link as RouterLink } from "react-router";
+import { cn } from "utils/cn";
+import { docs } from "utils/docs";
+
+type TaskWildcardWarningProps = {
+	className?: string;
+};
+
+export const TaskWildcardWarning = ({
+	className,
+}: TaskWildcardWarningProps) => {
+	const { permissions } = useAuthenticated();
+	const canEditDeploymentConfig = Boolean(permissions.editDeploymentConfig);
+
+	return (
+		<div className={cn("text-center", className)}>
+			<h3 className="font-medium text-content-primary text-base mb-3">Error</h3>
+			<div className="text-content-secondary text-sm flex flex-col gap-3 items-center">
+				<div className="px-4">
+					This application has{" "}
+					<code className="py-px px-1 bg-surface-tertiary rounded-sm text-content-primary">
+						subdomain = true
+					</code>
+					{canEditDeploymentConfig ? (
+						<>
+							, but subdomain applications are not configured. This application
+							won't be accessible until you configure the{" "}
+							<code className="py-px px-1 bg-surface-tertiary rounded-sm text-content-primary whitespace-nowrap">
+								--wildcard-access-url
+							</code>{" "}
+							flag when starting the Coder server.
+						</>
+					) : (
+						", which requires a Coder deployment with a Wildcard Access URL configured. Please contact your administrator."
+					)}
+				</div>
+				<Button size="sm" variant="outline" asChild>
+					<RouterLink to={docs("/admin/networking/wildcard-access-url")}>
+						<SquareArrowOutUpRightIcon />
+						Learn more about wildcard access URL
+					</RouterLink>
+				</Button>
+			</div>
+		</div>
+	);
+};