diff --git a/src/vs/editor/contrib/comment/common/lineCommentCommand.ts b/src/vs/editor/contrib/comment/common/lineCommentCommand.ts
index 9cf5de8659a..3311aa6ffae 100644
--- a/src/vs/editor/contrib/comment/common/lineCommentCommand.ts
+++ b/src/vs/editor/contrib/comment/common/lineCommentCommand.ts
@@ -63,34 +63,25 @@ export class LineCommentCommand implements editorCommon.ICommand {
 	 * Returns null if any of the lines doesn't support a line comment string.
 	 */
 	public static _gatherPreflightCommentStrings(model: editorCommon.ITokenizedModel, startLineNumber: number, endLineNumber: number): ILinePreflightData[] {
-		let commentStrForLanguage: string[] = [];
+
+		model.forceTokenization(startLineNumber);
+		const languageId = model.getLanguageIdAtPosition(startLineNumber, 1);
+
+		const config = LanguageConfigurationRegistry.getComments(languageId);
+		const commentStr = (config ? config.lineCommentToken : null);
+		if (!commentStr) {
+			// Mode does not support line comments
+			return null;
+		}
+
 		let lines: ILinePreflightData[] = [];
 		for (let i = 0, lineCount = endLineNumber - startLineNumber + 1; i < lineCount; i++) {
-			let lineNumber = startLineNumber + i;
-			model.forceTokenization(lineNumber);
-			let languageId = model.getLanguageIdAtPosition(lineNumber, 1);
-
-			// Find the commentStr for this line, if none is found then bail out: we cannot do line comments
-			let commentStr: string;
-			if (commentStrForLanguage[languageId]) {
-				commentStr = commentStrForLanguage[languageId];
-			} else {
-				let config = LanguageConfigurationRegistry.getComments(languageId);
-				commentStr = (config ? config.lineCommentToken : null);
-				if (!commentStr) {
-					// Mode does not support line comments
-					return null;
-				}
-
-				commentStrForLanguage[languageId] = commentStr;
-			}
-
-			lines.push({
+			lines[i] = {
 				ignore: false,
 				commentStr: commentStr,
 				commentStrOffset: 0,
 				commentStrLength: commentStr.length
-			});
+			};
 		}
 
 		return lines;
diff --git a/src/vs/editor/contrib/comment/test/common/lineCommentCommand.test.ts b/src/vs/editor/contrib/comment/test/common/lineCommentCommand.test.ts
index 802efd52419..1326d8bda33 100644
--- a/src/vs/editor/contrib/comment/test/common/lineCommentCommand.test.ts
+++ b/src/vs/editor/contrib/comment/test/common/lineCommentCommand.test.ts
@@ -9,6 +9,12 @@ import { Selection } from 'vs/editor/common/core/selection';
 import { ILinePreflightData, IPreflightData, ISimpleModel, LineCommentCommand, Type } from 'vs/editor/contrib/comment/common/lineCommentCommand';
 import { testCommand } from 'vs/editor/test/common/commands/commandTestUtils';
 import { CommentMode } from 'vs/editor/test/common/commentMode';
+import * as modes from 'vs/editor/common/modes';
+import { NULL_STATE } from 'vs/editor/common/modes/nullMode';
+import { TokenizationResult2 } from 'vs/editor/common/core/token';
+import { MockMode } from "vs/editor/test/common/mocks/mockMode";
+import { CommentRule } from "vs/editor/common/modes/languageConfiguration";
+import { LanguageConfigurationRegistry } from "vs/editor/common/modes/languageConfigurationRegistry";
 
 suite('Editor Contrib - Line Comment Command', () => {
 
@@ -827,4 +833,108 @@ suite('Editor Contrib - Line Comment As Block Comment 2', () => {
 	});
 });
 
+suite('Editor Contrib - Line Comment in mixed modes', () => {
 
+	const OUTER_LANGUAGE_ID = new modes.LanguageIdentifier('outerMode', 3);
+	const INNER_LANGUAGE_ID = new modes.LanguageIdentifier('innerMode', 4);
+
+	class OuterMode extends MockMode {
+		constructor(commentsConfig: CommentRule) {
+			super(OUTER_LANGUAGE_ID);
+			this._register(LanguageConfigurationRegistry.register(this.getLanguageIdentifier(), {
+				comments: commentsConfig
+			}));
+
+			this._register(modes.TokenizationRegistry.register(this.getLanguageIdentifier().language, {
+				getInitialState: (): modes.IState => NULL_STATE,
+				tokenize: undefined,
+				tokenize2: (line: string, state: modes.IState): TokenizationResult2 => {
+					let languageId = (/^  /.test(line) ? INNER_LANGUAGE_ID : OUTER_LANGUAGE_ID);
+
+					let tokens = new Uint32Array(1 << 1);
+					tokens[(0 << 1)] = 0;
+					tokens[(0 << 1) + 1] = (
+						(modes.ColorId.DefaultForeground << modes.MetadataConsts.FOREGROUND_OFFSET)
+						| (languageId.id << modes.MetadataConsts.LANGUAGEID_OFFSET)
+					);
+					return new TokenizationResult2(tokens, state);
+				}
+			}));
+		}
+	}
+
+	class InnerMode extends MockMode {
+		constructor(commentsConfig: CommentRule) {
+			super(INNER_LANGUAGE_ID);
+			this._register(LanguageConfigurationRegistry.register(this.getLanguageIdentifier(), {
+				comments: commentsConfig
+			}));
+		}
+	}
+
+	function testLineCommentCommand(lines: string[], selection: Selection, expectedLines: string[], expectedSelection: Selection): void {
+		let outerMode = new OuterMode({ lineComment: '//', blockComment: ['/*', '*/'] });
+		let innerMode = new InnerMode({ lineComment: null, blockComment: ['{/*', '*/}'] });
+		testCommand(
+			lines,
+			outerMode.getLanguageIdentifier(),
+			selection,
+			(sel) => new LineCommentCommand(sel, 4, Type.Toggle),
+			expectedLines,
+			expectedSelection
+		);
+		innerMode.dispose();
+		outerMode.dispose();
+	}
+
+	test('issue #24047 (part 1): Commenting code in JSX files', () => {
+		testLineCommentCommand(
+			[
+				'import React from \'react\';',
+				'const Loader = () => (',
+				'  <div>',
+				'    Loading...',
+				'  </div>',
+				');',
+				'export default Loader;'
+			],
+			new Selection(1, 1, 7, 22),
+			[
+				'// import React from \'react\';',
+				'// const Loader = () => (',
+				'//   <div>',
+				'//     Loading...',
+				'//   </div>',
+				'// );',
+				'// export default Loader;'
+			],
+			new Selection(1, 4, 7, 25),
+		);
+	});
+
+	test('issue #24047 (part 2): Commenting code in JSX files', () => {
+		testLineCommentCommand(
+			[
+				'import React from \'react\';',
+				'const Loader = () => (',
+				'  <div>',
+				'    Loading...',
+				'  </div>',
+				');',
+				'export default Loader;'
+			],
+			new Selection(3, 4, 3, 4),
+			[
+				'import React from \'react\';',
+				'const Loader = () => (',
+				'  {/*<div>*/}',
+				'    Loading...',
+				'  </div>',
+				');',
+				'export default Loader;'
+			],
+			new Selection(3, 7, 3, 7),
+		);
+	});
+
+});