diff --git a/src/factory.ts b/src/factory.ts
index 04ce03b3..b1726d48 100644
--- a/src/factory.ts
+++ b/src/factory.ts
@@ -571,7 +571,8 @@ export function defineCommand<T extends z.ZodType> (config: CommandConfig<T>): O
         const { simplifyZodIssues, formatIssuesText } = await import('./lib/zod-error.js')
         const issues = simplifyZodIssues(result.error.issues)
         if (jsonFormat === true) {
-          process.stderr.write(JSON.stringify({
+          const writeErr = cmd.configureOutput().writeErr ?? ((s: string) => process.stderr.write(s))
+          writeErr(JSON.stringify({
             error: {
               code: 'input_validation_failed',
               message: `Input validation failed with ${issues.length} issue(s)`,
diff --git a/test/factory.test.ts b/test/factory.test.ts
index e7100144..6e433355 100644
--- a/test/factory.test.ts
+++ b/test/factory.test.ts
@@ -1705,19 +1705,12 @@ describe('defineCommand', () => {
       prog.exitOverride()
       cmd.exitOverride()
       let out = ''
-      const origOut = process.stdout.write.bind(process.stdout)
-      const origErr = process.stderr.write.bind(process.stderr)
-      process.stdout.write = (chunk: unknown) => { out += String(chunk); return true }
-      process.stderr.write = (chunk: unknown) => { out += String(chunk); return true }
       prog.configureOutput({ writeOut: (s) => { out += s }, writeErr: (s) => { out += s } })
       cmd.configureOutput({ writeOut: (s) => { out += s }, writeErr: (s) => { out += s } })
       try {
         await prog.parseAsync(['--json', cmd.name(), ...argv], { from: 'user' })
       } catch {
         // exitOverride throws on cmd.error(); that's expected
-      } finally {
-        process.stdout.write = origOut
-        process.stderr.write = origErr
       }
       let parsed: unknown = null
       try { parsed = JSON.parse(out) } catch { /* not JSON - test will fail on assertion */ }