diff --git a/packages/langium/src/generator/template-string.ts b/packages/langium/src/generator/template-string.ts
index 8ab543115..2414d8cd1 100644
--- a/packages/langium/src/generator/template-string.ts
+++ b/packages/langium/src/generator/template-string.ts
@@ -57,7 +57,7 @@ export function expandToString(staticParts: TemplateStringsArray, ...substitutio
 }
 
 export const SNLE = Object.freeze('__«SKIP^NEW^LINE^IF^EMPTY»__');
-export const NEWLINE_REGEXP = /\r?\n/g;
+export const NEWLINE_REGEXP = /\r?\n/gm;
 const nonWhitespace = /\S|$/;
 
 // add the alignment of the previous static part to all lines of the following substitution
diff --git a/packages/langium/src/test/langium-test.ts b/packages/langium/src/test/langium-test.ts
index ff7bca00e..4a61f8aff 100644
--- a/packages/langium/src/test/langium-test.ts
+++ b/packages/langium/src/test/langium-test.ts
@@ -19,6 +19,7 @@ import * as assert from 'node:assert';
 import { stream } from '../utils/stream.js';
 import type { AsyncDisposable } from '../utils/disposable.js';
 import { Disposable } from '../utils/disposable.js';
+import { normalizeEOL } from '../generator/template-string.js';
 
 export interface ParseHelperOptions extends BuildOptions {
     /**
@@ -479,7 +480,7 @@ export function expectFormatting(services: LangiumServices): (expectedFormatting
             formatter.formatDocument(document, { options, textDocument: identifier }));
 
         const editedDocument = TextDocument.applyEdits(document.textDocument, edits);
-        expectedFunction(editedDocument, expectedFormatting.after);
+        expectedFunction(normalizeEOL(editedDocument), normalizeEOL(expectedFormatting.after));
 
         const disposable = Disposable.create(() => clearDocuments(services, [document]));
         if (expectedFormatting.disposeAfterCheck) {
diff --git a/packages/langium/test/grammar/lsp/grammar-formatter.test.ts b/packages/langium/test/grammar/lsp/grammar-formatter.test.ts
new file mode 100644
index 000000000..ca735739e
--- /dev/null
+++ b/packages/langium/test/grammar/lsp/grammar-formatter.test.ts
@@ -0,0 +1,63 @@
+/******************************************************************************
+* Copyright 2023 TypeFox GmbH
+* This program and the accompanying materials are made available under the
+* terms of the MIT License, which is available in the project root.
+******************************************************************************/
+
+import { describe, test } from 'vitest';
+import { EmptyFileSystem, createLangiumGrammarServices, expandToString } from 'langium';
+import { expectFormatting } from 'langium/test';
+
+const services = createLangiumGrammarServices(EmptyFileSystem);
+const formatting = expectFormatting(services.grammar);
+
+describe('Grammar Formatter', () => {
+
+    test('Indents interface properties', async () => {
+        await formatting({
+            before: expandToString`
+                interface Test {
+                // This is a comment
+                a: string
+                        b: number
+                            // This is another comment
+                            c: boolean
+                }
+            `,
+            after: expandToString`
+                interface Test {
+                    // This is a comment
+                    a: string
+                    b: number
+                    // This is another comment
+                    c: boolean
+                }
+            `
+        });
+    });
+
+    test('Formats interface extends references', async () => {
+        await formatting({
+            before: expandToString`
+                interface A extends   B,C,    D,E{}
+            `,
+            after: expandToString`
+                interface A extends B, C, D, E {
+                }
+            `
+        });
+    });
+
+    test('Formats union type definitions', async () => {
+        await formatting({
+            before: expandToString`
+                type A=    B | C | D
+                ;
+            `,
+            after: expandToString`
+                type A = B | C | D;
+            `
+        });
+    });
+
+});
diff --git a/packages/langium/test/grammar/lsp/langium-grammar-semantic-token-provider.test.ts b/packages/langium/test/grammar/lsp/grammar-semantic-token-provider.test.ts
similarity index 100%
rename from packages/langium/test/grammar/lsp/langium-grammar-semantic-token-provider.test.ts
rename to packages/langium/test/grammar/lsp/grammar-semantic-token-provider.test.ts