diff --git a/lib/core/src/server/build-dev.ts b/lib/core/src/server/build-dev.ts
index 684a0d1f1ba1..622df7aea7fe 100644
--- a/lib/core/src/server/build-dev.ts
+++ b/lib/core/src/server/build-dev.ts
@@ -153,8 +153,8 @@ function outputStartupInformation(options: {
   version: string;
   address: string;
   networkAddress: string;
-  managerTotalTime: [number, number];
-  previewTotalTime: [number, number];
+  managerTotalTime?: [number, number];
+  previewTotalTime?: [number, number];
 }) {
   const {
     updateInfo,
@@ -283,10 +283,9 @@ export async function buildDevStandalone(
 
     if (options.smokeTest) {
       await outputStats(previewStats, managerStats);
-      const managerWarnings = (managerStats as any).toJson().warnings.length > 0;
-      const previewWarnings =
-        !options.ignorePreview && (previewStats as any).toJson().warnings.length > 0;
-      process.exit(managerWarnings || previewWarnings ? 1 : 0);
+      const hasManagerWarnings = managerStats && managerStats.toJson().warnings.length > 0;
+      const hasPreviewWarnings = previewStats && previewStats.toJson().warnings.length > 0;
+      process.exit(hasManagerWarnings || (hasPreviewWarnings && !options.ignorePreview) ? 1 : 0);
       return;
     }
 
diff --git a/lib/core/src/server/dev-server.ts b/lib/core/src/server/dev-server.ts
index fce777198134..10e964d4f79f 100644
--- a/lib/core/src/server/dev-server.ts
+++ b/lib/core/src/server/dev-server.ts
@@ -258,7 +258,7 @@ const startManager = async ({
   }
 
   if (!managerConfig) {
-    return { managerStats: null, managerTotalTime: [0, 0] } as ManagerResult;
+    return {};
   }
 
   const compiler = webpack(managerConfig);
@@ -311,7 +311,7 @@ const startPreview = async ({
   outputDir,
 }: any): Promise<PreviewResult> => {
   if (options.ignorePreview) {
-    return { previewStats: null, previewTotalTime: [0, 0] } as PreviewResult;
+    return {};
   }
 
   const previewConfig = await loadConfig({
diff --git a/lib/core/src/server/types.ts b/lib/core/src/server/types.ts
index 6993a9dd0dbf..bcd4062089fc 100644
--- a/lib/core/src/server/types.ts
+++ b/lib/core/src/server/types.ts
@@ -94,13 +94,13 @@ export interface ReleaseNotesData {
 }
 
 export interface PreviewResult {
-  previewStats: Stats;
-  previewTotalTime: [number, number];
+  previewStats?: Stats;
+  previewTotalTime?: [number, number];
 }
 
 export interface ManagerResult {
-  managerStats: Stats;
-  managerTotalTime: [number, number];
+  managerStats?: Stats;
+  managerTotalTime?: [number, number];
 }
 
 // TODO: this is a generic interface that we can share across multiple SB packages (like @storybook/cli)