diff --git a/CLAUDE.md b/CLAUDE.md
index 22912ea..57e9dbf 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -13,7 +13,7 @@ Transcript-based shell integration test runner. Bun + TypeScript.
   - `--path <path>` — prepend to `$PATH` (repeatable)
   - `--timeout <dur>` — per-command timeout (default `10s`)
   - `-v, --verbose` — print each command as it runs
-  - `--port-from <n>` — auto-assign `$PORT` starting from n
+  - `--port-from <n>` — auto-assign `$PORT` starting from n (default `5400`)
   - `--parallel` — run files in parallel
 
 ## Architecture
diff --git a/src/cli/index.ts b/src/cli/index.ts
index 63e4c63..34f4277 100755
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -79,7 +79,7 @@ program
   .option("--path <path>", "Prepend <path> to PATH (repeatable)", (val: string, acc: string[]) => [...acc, val], [])
   .option("--timeout <dur>", "Per-command timeout", "10s")
   .option("-v, --verbose", "Print each command as it runs")
-  .option("--port-from <n>", "Auto-assign $PORT starting from <n>")
+  .option("--port-from <n>", "Auto-assign $PORT starting from <n>", "5400")
   .option("--parallel", "Run files in parallel")
   .action(async (fileArgs: string[], opts) => {
     const timeoutMs = parseDuration(opts.timeout)
@@ -94,14 +94,14 @@ program
     const start = performance.now()
     const results: TestResult[] = []
     const cwd = process.cwd()
-    const portFrom = opts.portFrom ? parseInt(opts.portFrom, 10) : undefined
-    if (portFrom !== undefined && Number.isNaN(portFrom)) {
+    const portFrom = parseInt(opts.portFrom, 10)
+    if (Number.isNaN(portFrom)) {
       console.error("--port-from must be an integer")
       process.exit(1)
     }
     let nextPort = portFrom
 
-    const runOne = async (filePath: string, port: number | undefined) => {
+    const runOne = async (filePath: string, port: number) => {
       const content = await readFile(filePath, "utf-8")
       const parsed = parse(relative(cwd, filePath), content)
 
@@ -125,7 +125,7 @@ program
         }
       }
       Object.assign(envVars, setupEnvVars, userEnvVars)
-      if (port !== undefined && !("PORT" in userEnvVars) && !("PORT" in setupEnvVars)) {
+      if (!("PORT" in userEnvVars) && !("PORT" in setupEnvVars)) {
         envVars["PORT"] = String(port)
       }
       const merged: ShoutFile = { ...parsed, commands: [...setupCommands, ...parsed.commands] }
@@ -205,7 +205,7 @@ program
     }
 
     if (opts.parallel) {
-      const all = await Promise.all(files.map(f => runOne(f, nextPort !== undefined ? nextPort++ : undefined)))
+      const all = await Promise.all(files.map(f => runOne(f, nextPort++)))
       for (const r of all) {
         printDots(r)
         results.push(r)
@@ -213,7 +213,7 @@ program
       process.stdout.write("\n")
     } else {
       for (const filePath of files) {
-        const r = await runOne(filePath, nextPort !== undefined ? nextPort++ : undefined)
+        const r = await runOne(filePath, nextPort++)
         printDots(r)
         results.push(r)
       }