diff --git a/src/linter/ui5Types/SourceFileLinter.ts b/src/linter/ui5Types/SourceFileLinter.ts
index 1fe6d39dc..70494d193 100644
--- a/src/linter/ui5Types/SourceFileLinter.ts
+++ b/src/linter/ui5Types/SourceFileLinter.ts
@@ -28,7 +28,7 @@ export default class SourceFileLinter {
 	constructor(
 		context: LinterContext, resourcePath: ResourcePath, sourceFile: ts.SourceFile, sourceMap: string | undefined,
 		checker: ts.TypeChecker, reportCoverage: boolean | undefined = false,
-		messageDetails: boolean | undefined = false, manifestContent: string | undefined
+		messageDetails: boolean | undefined = false, manifestContent?: string | undefined
 	) {
 		this.#resourcePath = resourcePath;
 		this.#sourceFile = sourceFile;
@@ -498,16 +498,16 @@ export default class SourceFileLinter {
 
 		if (manifestJson.manifest?.value === "\"json\"") { // The manifest is an external manifest.json file
 			const parsedManifestContent =
-				JSON.parse(this.#manifestContent ?? "") as SAPJSONSchemaForWebApplicationManifestFile;
+				JSON.parse(this.#manifestContent ?? "{}") as SAPJSONSchemaForWebApplicationManifestFile;
 
 			const {rootView, routing} = parsedManifestContent["sap.ui5"] ?? {} as JSONSchemaForSAPUI5Namespace;
 			// @ts-expect-error async is part of RootViewDefFlexEnabled and RootViewDef
 			rootViewAsyncFlag = rootView?.async as boolean;
 			routingAsyncFlag = routing?.config?.async;
 		} else {
-			/* eslint-disable  @typescript-eslint/no-explicit-any */
+			/* eslint-disable @typescript-eslint/no-explicit-any */
 			const instanceOfPropsRecord = (obj: any): obj is propsRecord => {
-				return obj && typeof obj === "object";
+				return !!obj && typeof obj === "object";
 			};
 
 			let manifestSapui5Section: propsRecord | undefined;
diff --git a/test/lib/linter/_linterHelper.ts b/test/lib/linter/_linterHelper.ts
index 60d21dce0..9decba71a 100644
--- a/test/lib/linter/_linterHelper.ts
+++ b/test/lib/linter/_linterHelper.ts
@@ -28,11 +28,12 @@ export async function esmockDeprecationText() {
 			context: LinterContext, filePath: string, sourceFile: SourceFile,
 			sourceMap: string | undefined, checker: TypeChecker,
 			reportCoverage: boolean | undefined = false,
-			messageDetails: boolean | undefined = false
+			messageDetails: boolean | undefined = false,
+			manifestContent?: string | undefined
 		) {
 			// Don't use sinon's stubs as it's hard to clean after them in this case and it leaks memory.
 			const linter = new SourceFileLinter(
-				context, filePath, sourceFile, sourceMap, checker, reportCoverage, messageDetails
+				context, filePath, sourceFile, sourceMap, checker, reportCoverage, messageDetails, manifestContent
 			);
 			linter.getDeprecationText = () => "Deprecated test message";
 			return linter;
diff --git a/test/lib/linter/snapshots/linter.ts.md b/test/lib/linter/snapshots/linter.ts.md
index ab8fd7ad9..ee1ec1b18 100644
--- a/test/lib/linter/snapshots/linter.ts.md
+++ b/test/lib/linter/snapshots/linter.ts.md
@@ -271,8 +271,27 @@ Generated by [AVA](https://avajs.dev).
         errorCount: 0,
         fatalErrorCount: 0,
         filePath: 'webapp/Component.js',
-        messages: [],
-        warningCount: 0,
+        messages: [
+          {
+            column: 9,
+            fatal: undefined,
+            line: 4,
+            message: 'Remove the async flag for "sap.ui5/rootView" from the manifest',
+            messageDetails: 'https://sapui5.hana.ondemand.com/#/api/sap.ui.core.IAsyncContentCreation',
+            ruleId: 'ui5-linter-no-sync-loading',
+            severity: 1,
+          },
+          {
+            column: 9,
+            fatal: undefined,
+            line: 4,
+            message: 'Remove the async flag for "sap.ui5/routing/config" from the manifest',
+            messageDetails: 'https://sapui5.hana.ondemand.com/#/api/sap.ui.core.IAsyncContentCreation',
+            ruleId: 'ui5-linter-no-sync-loading',
+            severity: 1,
+          },
+        ],
+        warningCount: 2,
       },
       {
         coverageInfo: [
@@ -745,6 +764,33 @@ Generated by [AVA](https://avajs.dev).
 > Snapshot 1
 
     [
+      {
+        coverageInfo: [],
+        errorCount: 0,
+        fatalErrorCount: 0,
+        filePath: 'webapp/Component.js',
+        messages: [
+          {
+            column: 9,
+            fatal: undefined,
+            line: 4,
+            message: 'Remove the async flag for "sap.ui5/rootView" from the manifest',
+            messageDetails: 'https://sapui5.hana.ondemand.com/#/api/sap.ui.core.IAsyncContentCreation',
+            ruleId: 'ui5-linter-no-sync-loading',
+            severity: 1,
+          },
+          {
+            column: 9,
+            fatal: undefined,
+            line: 4,
+            message: 'Remove the async flag for "sap.ui5/routing/config" from the manifest',
+            messageDetails: 'https://sapui5.hana.ondemand.com/#/api/sap.ui.core.IAsyncContentCreation',
+            ruleId: 'ui5-linter-no-sync-loading',
+            severity: 1,
+          },
+        ],
+        warningCount: 2,
+      },
       {
         coverageInfo: [],
         errorCount: 1,
diff --git a/test/lib/linter/snapshots/linter.ts.snap b/test/lib/linter/snapshots/linter.ts.snap
index 4dafd76ff..33f8aa210 100644
Binary files a/test/lib/linter/snapshots/linter.ts.snap and b/test/lib/linter/snapshots/linter.ts.snap differ