diff --git a/packages/rstack/src/cli/commands.ts b/packages/rstack/src/cli/commands.ts
index 4368dbea..891f67d5 100644
--- a/packages/rstack/src/cli/commands.ts
+++ b/packages/rstack/src/cli/commands.ts
@@ -1,4 +1,5 @@
 import { join, resolve } from 'node:path';
+import { pathToFileURL } from 'node:url';
 import { getConfigState } from '../config.ts';
 import { insertConfigArg, parseArgs, parseCliArgs } from './args.ts';
 import { hasHelpFlag, printCommandHelp } from './help.ts';
@@ -138,6 +139,8 @@ async function runRspressCLI(args: string[]): Promise<void> {
   }
 }
 
+const RSLINT_CONFIG_PATH = join(import.meta.dirname, 'rslintConfig.js');
+
 async function runRslintCLI(args: string[]): Promise<void> {
   if (hasHelpFlag(args)) {
     return printCommandHelp('lint');
@@ -146,11 +149,7 @@ async function runRslintCLI(args: string[]): Promise<void> {
   const argv = [
     process.execPath,
     'rslint',
-    ...insertConfigArg(
-      args,
-      '--config',
-      join(import.meta.dirname, 'rslintConfig.js'),
-    ),
+    ...insertConfigArg(args, '--config', RSLINT_CONFIG_PATH),
   ];
 
   const { runCLI } = await import('@rslint/core');
@@ -177,11 +176,16 @@ async function runCheckCLI(args: string[]): Promise<void> {
     return;
   }
 
+  // Rslint loads its one-shot config through Node's module cache. Import the
+  // same URL to read the Rstack config exported for the following fmt phase.
+  const { loadedConfig } = (await import(
+    pathToFileURL(RSLINT_CONFIG_PATH).href
+  )) as typeof import('../rslintConfig.ts');
   const { runFmtCLI } = await import(
     /* rspackChunkName: 'fmt' */
     '../fmt/cli.ts'
   );
-  await runFmtCLI(['--check']);
+  await runFmtCLI(['--check'], { loadedConfig });
 }
 
 export async function setupCommands(): Promise<void> {
diff --git a/packages/rstack/src/fmt/cli.ts b/packages/rstack/src/fmt/cli.ts
index 7b13f498..0eb4e626 100644
--- a/packages/rstack/src/fmt/cli.ts
+++ b/packages/rstack/src/fmt/cli.ts
@@ -3,7 +3,7 @@ import { performance } from 'node:perf_hooks';
 import { color, logger } from 'rslog';
 import { parseArgs } from '../cli/args.ts';
 import { printCommandHelp } from '../cli/help.ts';
-import { loadRstackConfig } from '../config.ts';
+import { loadRstackConfig, type LoadedRstackConfig } from '../config.ts';
 import { ensureProjectCacheDir } from '../projectCache.ts';
 import { fmtCacheFileName } from './cacheStore.ts';
 import { resolveFmtConfig } from './config.ts';
@@ -29,6 +29,11 @@ interface ParsedFmtCLIArgs {
   lsp: boolean;
 }
 
+type RunFmtCLIOptions = {
+  /** Rstack config already loaded by the lint phase of `rs check`. */
+  loadedConfig?: LoadedRstackConfig;
+};
+
 const parseMaxWorkers = (value: string | undefined): number | undefined => {
   if (value === undefined) {
     return undefined;
@@ -255,8 +260,12 @@ const logFmtResult = (
   }
 };
 
-const loadFmtConfig = async (cwd: string): Promise<ResolvedFmtConfig> => {
-  const { configs, filePath } = await loadRstackConfig({ cwd });
+const loadFmtConfig = async (
+  cwd: string,
+  loadedConfig?: LoadedRstackConfig,
+): Promise<ResolvedFmtConfig> => {
+  const { configs, filePath } =
+    loadedConfig ?? (await loadRstackConfig({ cwd }));
 
   return resolveFmtConfig({
     definition: configs.fmt,
@@ -265,7 +274,10 @@ const loadFmtConfig = async (cwd: string): Promise<ResolvedFmtConfig> => {
   });
 };
 
-const runFmtCLI = async (args: string[]): Promise<void> => {
+const runFmtCLI = async (
+  args: string[],
+  { loadedConfig }: RunFmtCLIOptions = {},
+): Promise<void> => {
   const cwd = process.cwd();
   const startTime = performance.now();
 
@@ -337,7 +349,7 @@ const runFmtCLI = async (args: string[]): Promise<void> => {
       }
     }
 
-    const config = await loadFmtConfig(cwd);
+    const config = await loadFmtConfig(cwd, loadedConfig);
     const files = await discoverFmtFiles({
       cwd,
       patterns,
diff --git a/packages/rstack/src/rslintConfig.ts b/packages/rstack/src/rslintConfig.ts
index 50f13c20..2a0cb25f 100644
--- a/packages/rstack/src/rslintConfig.ts
+++ b/packages/rstack/src/rslintConfig.ts
@@ -1,7 +1,10 @@
-import { loadRstackConfig } from './config.ts';
+import { loadRstackConfig, type LoadedRstackConfig } from './config.ts';
 import type { RslintConfig } from '@rslint/core';
 
-const { configs } = await loadRstackConfig();
+// Expose the loaded config so `rs check` can pass it to fmt instead of loading
+// and executing the Rstack config a second time.
+export const loadedConfig: LoadedRstackConfig = await loadRstackConfig();
+const { configs } = loadedConfig;
 const lintDefinition = configs.lint ?? [];
 
 let lintConfig: RslintConfig;