diff --git a/src/vs/editor/common/modes/languageConfigurationRegistry.ts b/src/vs/editor/common/modes/languageConfigurationRegistry.ts
index 6074e34cc22..8f42df68d9d 100644
--- a/src/vs/editor/common/modes/languageConfigurationRegistry.ts
+++ b/src/vs/editor/common/modes/languageConfigurationRegistry.ts
@@ -729,7 +729,7 @@ export class LanguageConfigurationRegistryImpl {
 			} else {
 				appendText = '';
 			}
-		} else if (indentAction === IndentAction.Indent) {
+		} else if (indentAction === IndentAction.Indent || indentAction === IndentAction.IndentOutdent) {
 			appendText = '\t' + appendText;
 		}
 
diff --git a/src/vs/editor/test/browser/controller/cursor.test.ts b/src/vs/editor/test/browser/controller/cursor.test.ts
index 5b3dcecfe87..1bb64e4d511 100644
--- a/src/vs/editor/test/browser/controller/cursor.test.ts
+++ b/src/vs/editor/test/browser/controller/cursor.test.ts
@@ -2812,6 +2812,38 @@ suite('Editor Controller - Cursor Configuration', () => {
 		mode.dispose();
 	});
 
+	test('issue #115148: indentOutdent and appendText', () => {
+		const mode = new class extends MockMode {
+			constructor() {
+				super(new LanguageIdentifier('onEnterMode', 3));
+				this._register(LanguageConfigurationRegistry.register(this.getLanguageIdentifier(), {
+					onEnterRules: [{
+						beforeText: /.*/,
+						action: {
+							indentAction: IndentAction.IndentOutdent,
+							appendText: 'x'
+						}
+					}]
+				}));
+			}
+		}();
+		usingCursor({
+			text: [
+				'text {}'
+			],
+			languageIdentifier: mode.getLanguageIdentifier(),
+		}, (editor, model, viewModel) => {
+
+			moveTo(editor, viewModel, 1, 7);
+			viewModel.type('\n', 'keyboard');
+			assert.strictEqual(model.getLineContent(1), 'text {');
+			assert.strictEqual(model.getLineContent(2), '    x');
+			assert.strictEqual(model.getLineContent(3), '}');
+			assertCursor(viewModel, new Position(2, 6));
+		});
+		mode.dispose();
+	});
+
 	test('issue #6862: Editor removes auto inserted indentation when formatting on type', () => {
 		let mode = new OnEnterMode(IndentAction.IndentOutdent);
 		usingCursor({