diff --git a/schemas/report/v4.json b/schemas/report/v4.json
index d7f00e7..a6ac675 100644
--- a/schemas/report/v4.json
+++ b/schemas/report/v4.json
@@ -110,7 +110,6 @@
     "details": {
       "type": "array",
       "minItems": 1,
-      "uniqueItems": true,
       "items": {
         "type": "object",
         "unevaluatedProperties": false,
diff --git a/src/helpers/report.cjs b/src/helpers/report.cjs
index fe07197..b269874 100644
--- a/src/helpers/report.cjs
+++ b/src/helpers/report.cjs
@@ -31,6 +31,26 @@ const getReportVersion = (report) => {
 	}
 };
 
+const validateReportV4Details = (report, dataVar) => {
+	const detailIndices = new Map();
+
+	for (const [index, detail] of report.details.entries()) {
+		const key = detail.testId === undefined ?
+			`detail:${JSON.stringify(detail)}` :
+			`testId:${detail.testId}`;
+		const existingIndex = detailIndices.get(key);
+
+		if (existingIndex !== undefined) {
+			throw new Error(
+				`[${dataVar}].details: must NOT have duplicate items ` +
+				`(items ## ${existingIndex} and ${index} are identical)`
+			);
+		}
+
+		detailIndices.set(key, index);
+	}
+};
+
 const validateReport = (report, dataVar = 'report') => {
 	const reportVersion = getReportVersion(report);
 	let errors;
@@ -59,6 +79,10 @@ const validateReport = (report, dataVar = 'report') => {
 				errors = validateReportV4Ajv.errors;
 			}
 
+			if (errors === undefined || errors.length === 0) {
+				validateReportV4Details(report, dataVar);
+			}
+
 			break;
 		default:
 			throw new Error(`Unknown report version '${reportVersion}'`);
diff --git a/test/unit/report.test.js b/test/unit/report.test.js
index 92bd98f..603ddf8 100644
--- a/test/unit/report.test.js
+++ b/test/unit/report.test.js
@@ -403,6 +403,14 @@ const testReportOldV3ConfigOnly = {
 	...testReportOldV3Full,
 	details: testDetailsOldV3ConfigOnly
 };
+const testReportV4Full = {
+	...testReportLatestFull,
+	version: 4,
+	details: testDetailsLatest.map((detail, index) => ({
+		...detail,
+		testId: `test-id-${index}`
+	}))
+};
 
 describe('report', () => {
 	afterEach(() => mock.reset());
@@ -840,6 +848,47 @@ describe('report', () => {
 		});
 	});
 
+	describe('v4', () => {
+		it('allows otherwise identical details with distinct test IDs', () => {
+			const detail = testDetailsLatest[0];
+			const reportData = {
+				...testReportV4Full,
+				details: [{ ...detail, testId: 'test-id-1' }, { ...detail, testId: 'test-id-2' }]
+			};
+
+			mock.method(fs, 'readFileSync', () => JSON.stringify(reportData));
+
+			expect(() => new Report(testReportPath)).to.not.throw();
+		});
+
+		it('rejects duplicate test IDs', () => {
+			const detail = testDetailsLatest[0];
+			const reportData = {
+				...testReportV4Full,
+				details: [
+					{ ...detail, testId: 'duplicate-test-id' },
+					{ ...detail, duration: { final: 238, total: 550 }, testId: 'duplicate-test-id' }
+				]
+			};
+
+			mock.method(fs, 'readFileSync', () => JSON.stringify(reportData));
+
+			expect(() => new Report(testReportPath)).to.throw(/must NOT have duplicate items/);
+		});
+
+		it('rejects duplicate details without test IDs', () => {
+			const detail = testDetailsLatest[0];
+			const reportData = {
+				...testReportV4Full,
+				details: [detail, detail]
+			};
+
+			mock.method(fs, 'readFileSync', () => JSON.stringify(reportData));
+
+			expect(() => new Report(testReportPath)).to.throw(/must NOT have duplicate items/);
+		});
+	});
+
 	describe(`legacy (old v3, cleans to v${latestReportVersion})`, () => {
 		it('cleans config to configuration', () => {
 			mock.method(fs, 'readFileSync', () => JSON.stringify(testReportOldV3ConfigOnly));