diff --git a/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts b/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
index d25c8dfe06d..bf2bbb30e97 100644
--- a/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
+++ b/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
@@ -107,18 +107,24 @@ export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextD
 		// get start and end locations and create substrings
 		const start = this.locationAt(range.start);
 		const end = this.locationAt(range.end);
-		const startCell = this._cells[this._cellUris.get(start.uri) ?? -1];
-		const endCell = this._cells[this._cellUris.get(end.uri) ?? -1];
 
-		if (!startCell || !endCell) {
+		const startIdx = this._cellUris.get(start.uri);
+		const endIdx = this._cellUris.get(end.uri);
+
+		if (startIdx === undefined || endIdx === undefined) {
 			return '';
-		} else if (startCell === endCell) {
-			return startCell.document.getText(new types.Range(start.range.start, end.range.end));
-		} else {
-			const a = startCell.document.getText(new types.Range(start.range.start, new types.Position(startCell.document.lineCount, 0)));
-			const b = endCell.document.getText(new types.Range(new types.Position(0, 0), end.range.end));
-			return a + '\n' + b;
 		}
+
+		if (startIdx === endIdx) {
+			return this._cells[startIdx].document.getText(new types.Range(start.range.start, end.range.end));
+		}
+
+		const parts = [this._cells[startIdx].document.getText(new types.Range(start.range.start, new types.Position(this._cells[startIdx].document.lineCount, 0)))];
+		for (let i = startIdx + 1; i < endIdx; i++) {
+			parts.push(this._cells[i].document.getText());
+		}
+		parts.push(this._cells[endIdx].document.getText(new types.Range(new types.Position(0, 0), end.range.end)));
+		return parts.join('\n');
 	}
 
 	offsetAt(position: vscode.Position): number {
diff --git a/src/vs/workbench/test/browser/api/extHostNotebookConcatDocument.test.ts b/src/vs/workbench/test/browser/api/extHostNotebookConcatDocument.test.ts
index c38867cc9eb..b9c704ae5bf 100644
--- a/src/vs/workbench/test/browser/api/extHostNotebookConcatDocument.test.ts
+++ b/src/vs/workbench/test/browser/api/extHostNotebookConcatDocument.test.ts
@@ -536,19 +536,28 @@ suite('NotebookConcatDocument', function () {
 						language: 'test',
 						cellKind: CellKind.Code,
 						outputs: [],
+					}, {
+						handle: 3,
+						uri: CellUri.generate(notebook.uri, 3),
+						source: ['Three', 'Drei', 'Drüü'],
+						eol: '\n',
+						language: 'test',
+						cellKind: CellKind.Code,
+						outputs: [],
 					}]]]
 				}
 			]
 		}, false);
 
-		assert.strictEqual(notebook.apiNotebook.cellCount, 1 + 2); // markdown and code
+		assert.strictEqual(notebook.apiNotebook.cellCount, 1 + 3); // markdown and code
 
 		let doc = new ExtHostNotebookConcatDocument(extHostNotebooks, extHostDocuments, notebook.apiNotebook, undefined);
-		assertLines(doc, 'Hello', 'World', 'Hello World!', 'Hallo', 'Welt', 'Hallo Welt!');
+		assertLines(doc, 'Hello', 'World', 'Hello World!', 'Hallo', 'Welt', 'Hallo Welt!', 'Three', 'Drei', 'Drüü');
 
 		assert.strictEqual(doc.getText(new Range(0, 0, 0, 0)), '');
 		assert.strictEqual(doc.getText(new Range(0, 0, 1, 0)), 'Hello\n');
 		assert.strictEqual(doc.getText(new Range(2, 0, 4, 0)), 'Hello World!\nHallo\n');
+		assert.strictEqual(doc.getText(new Range(2, 0, 8, 0)), 'Hello World!\nHallo\nWelt\nHallo Welt!\nThree\nDrei\n');
 	});
 
 	test('validateRange/Position', function () {