diff --git a/packages/rstack/src/fmt/ignore.ts b/packages/rstack/src/fmt/ignore.ts
index bc814a5..1405de2 100644
--- a/packages/rstack/src/fmt/ignore.ts
+++ b/packages/rstack/src/fmt/ignore.ts
@@ -9,7 +9,7 @@ import type { ResolvedFmtConfig } from './types.ts';
  * Prettier already skips other generated lock files when it cannot infer a parser, so this list
  * contains only the additional defaults owned by `rs fmt`.
  */
-const defaultIgnorePatterns = ['package-lock.json', 'pnpm-lock.yaml'];
+const defaultIgnoreNames = ['package-lock.json', 'pnpm-lock.yaml'];
 
 type IgnoreMatcher = (filePath: string, isDirectory?: boolean) => boolean;
 
@@ -20,6 +20,12 @@ interface CreateIgnoreMatcherOptions {
   ignorePaths?: string[];
 }
 
+const createDefaultIgnoreMatcher = (): IgnoreMatcher => {
+  const suffixes = defaultIgnoreNames.map((name) => `${path.sep}${name}`);
+
+  return (filePath) => suffixes.some((suffix) => filePath.endsWith(suffix));
+};
+
 const createPatternMatcher = (rootPath: string, patterns: string): IgnoreMatcher => {
   const matcher = createIgnore({ allowRelativePaths: true }).add(patterns);
   const rootPrefix = rootPath.endsWith(path.sep) ? rootPath : `${rootPath}${path.sep}`;
@@ -58,10 +64,12 @@ const createIgnoreMatcher = async ({
   cwd,
   ignorePaths = [],
 }: CreateIgnoreMatcherOptions): Promise<IgnoreMatcher> => {
-  const configMatcher = createPatternMatcher(
-    config.rootPath,
-    [...defaultIgnorePatterns, ...config.ignorePatterns].join('\n'),
-  );
+  const configMatcher = config.ignorePatterns.length
+    ? createPatternMatcher(
+        config.rootPath,
+        [...defaultIgnoreNames, ...config.ignorePatterns].join('\n'),
+      )
+    : createDefaultIgnoreMatcher();
   if (ignorePaths.length === 0) {
     return configMatcher;
   }
diff --git a/packages/rstack/tests/fmt/ignore.test.ts b/packages/rstack/tests/fmt/ignore.test.ts
index 5826767..1d03361 100644
--- a/packages/rstack/tests/fmt/ignore.test.ts
+++ b/packages/rstack/tests/fmt/ignore.test.ts
@@ -64,6 +64,9 @@ test('ignores common lock files by default and allows explicit negation', async
 
   expect(isIgnored(path.join(rootPath, 'package-lock.json'))).toBe(true);
   expect(isIgnored(path.join(rootPath, 'packages/app/pnpm-lock.yaml'))).toBe(true);
+  expect(isIgnored(path.join(rootPath, 'packages/app/PNPM-LOCK.YAML'))).toBe(false);
+  expect(isIgnored(path.join(rootPath, '../shared/pnpm-lock.yaml'))).toBe(true);
+  expect(isIgnored(path.join(rootPath, 'pnpm-lock.yaml.backup'))).toBe(false);
   expect(isIgnoredAfterReinclude(path.join(rootPath, 'pnpm-lock.yaml'))).toBe(false);
 });