diff --git a/extensions/copilot/src/extension/tools/node/readFileTool.tsx b/extensions/copilot/src/extension/tools/node/readFileTool.tsx
index 06fb90b9192..359d5995dcd 100644
--- a/extensions/copilot/src/extension/tools/node/readFileTool.tsx
+++ b/extensions/copilot/src/extension/tools/node/readFileTool.tsx
@@ -22,6 +22,7 @@ import { IWorkspaceService } from '../../../platform/workspace/common/workspaceS
 import { getCachedSha256Hash } from '../../../util/common/crypto';
 import { clamp } from '../../../util/vs/base/common/numbers';
 import { dirname, extUriBiasedIgnorePathCase } from '../../../util/vs/base/common/resources';
+import { isHighSurrogate, isLowSurrogate } from '../../../util/vs/base/common/strings';
 import { sendSkillContentReadTelemetry } from '../common/skillTelemetry';
 import { URI } from '../../../util/vs/base/common/uri';
 import { IInstantiationService } from '../../../util/vs/platform/instantiation/common/instantiation';
@@ -432,7 +433,11 @@ class ReadFileResult extends PromptElement<ReadFileResultProps> {
 		let contents = rawContents.split('\n').map(line => {
 			if (line.length > MAX_LINE_LENGTH) {
 				hadLongLines = true;
-				return line.slice(0, MAX_LINE_LENGTH) + ' [truncated]';
+				let end = MAX_LINE_LENGTH;
+				if (isHighSurrogate(line.charCodeAt(end - 1)) && isLowSurrogate(line.charCodeAt(end))) {
+					end--;
+				}
+				return line.slice(0, end) + ' [truncated]';
 			}
 			return line;
 		}).join('\n');
diff --git a/extensions/copilot/src/extension/tools/node/test/readFile.spec.tsx b/extensions/copilot/src/extension/tools/node/test/readFile.spec.tsx
index 7e8206e2e47..548aeaf443b 100644
--- a/extensions/copilot/src/extension/tools/node/test/readFile.spec.tsx
+++ b/extensions/copilot/src/extension/tools/node/test/readFile.spec.tsx
@@ -42,13 +42,15 @@ suite('ReadFile', () => {
 		const longLine = 'x'.repeat(2500);
 		const longLinesContent = `normal line\n${longLine}\nanother normal line\n${longLine}`;
 		const longLinesDoc = createTextDocumentData(URI.file('/workspace/longlines.ts'), longLinesContent, 'ts').document;
+		const surrogateBoundaryLine = 'x'.repeat(1999) + '\u{1F6E1}' + 'tail';
+		const surrogateBoundaryDoc = createTextDocumentData(URI.file('/workspace/surrogate-boundary.ts'), surrogateBoundaryLine, 'ts').document;
 
 		const services = createExtensionUnitTestingServices();
 		services.define(IWorkspaceService, new SyncDescriptor(
 			TestWorkspaceService,
 			[
 				[URI.file('/workspace')],
-				[testDoc, emptyDoc, whitespaceDoc, singleLineDoc, largeDoc, longLinesDoc],
+				[testDoc, emptyDoc, whitespaceDoc, singleLineDoc, largeDoc, longLinesDoc, surrogateBoundaryDoc],
 			]
 		));
 		accessor = services.createTestingAccessor();
@@ -208,6 +210,18 @@ suite('ReadFile', () => {
 			}
 		});
 
+		test('long line truncation does not split surrogate pairs', async () => {
+			const toolsService = accessor.get(IToolsService);
+			const input: IReadFileParamsV2 = {
+				filePath: '/workspace/surrogate-boundary.ts'
+			};
+			const result = await toolsService.invokeTool(ToolName.ReadFile, { input, toolInvocationToken: null as never }, CancellationToken.None);
+			const resultString = await toolResultToString(accessor, result);
+			const truncatedLine = resultString.split('\n').find(line => line.endsWith(' [truncated]'));
+
+			expect(truncatedLine).toBe('x'.repeat(1999) + ' [truncated]');
+		});
+
 		test('read file with offset beyond file line count should throw error', async () => {
 			const toolsService = accessor.get(IToolsService);