diff --git a/lib/dispatcher/client.js b/lib/dispatcher/client.js
index 705b43b88bd..15a2089839e 100644
--- a/lib/dispatcher/client.js
+++ b/lib/dispatcher/client.js
@@ -237,7 +237,7 @@ class Client extends DispatcherBase {
           throw new InvalidArgumentError('h2Options.settings.initialWindowSize must be a positive integer, greater than 0')
         }
 
-        if (h2Options.maxConcurrentStreams != null && (!Number.isInteger(h2Options.connectionWindowSize) || h2Options.maxConcurrentStreams < 1)) {
+        if (h2Options.maxConcurrentStreams != null && (!Number.isInteger(h2Options.maxConcurrentStreams) || h2Options.maxConcurrentStreams < 1)) {
           throw new InvalidArgumentError('h2Options.maxConcurrentStreams must be a positive integer, greater than 0')
         }
 
@@ -331,7 +331,7 @@ class Client extends DispatcherBase {
         //   especially on high-latency networks. This matches common production HTTP/2 servers.
         // - connectionWindowSize: 524288 (512KB) vs Node.js default (none set)
         //   Provides better flow control for the entire connection across multiple streams.
-        initialWindowSize: h2Options?.initialWindowSize ?? initialWindowSize ?? 262144
+        initialWindowSize: h2Options?.settings?.initialWindowSize ?? initialWindowSize ?? 262144
       }
     }
 
diff --git a/test/http2-options.js b/test/http2-options.js
new file mode 100644
index 00000000000..0523227839b
--- /dev/null
+++ b/test/http2-options.js
@@ -0,0 +1,44 @@
+'use strict'
+
+const { tspl } = require('@matteo.collina/tspl')
+const { test } = require('node:test')
+const { Client } = require('..')
+const { kHTTP2Options } = require('../lib/core/symbols')
+
+test('h2Options.maxConcurrentStreams is validated on its own value', async (t) => {
+  t = tspl(t, { plan: 4 })
+
+  const client = new Client('https://localhost', {
+    h2Options: { maxConcurrentStreams: 10 }
+  })
+  t.strictEqual(client[kHTTP2Options].maxConcurrentStreams, 10)
+  await client.close()
+
+  const withWindow = new Client('https://localhost', {
+    h2Options: { maxConcurrentStreams: 10, connectionWindowSize: 65535 }
+  })
+  t.strictEqual(withWindow[kHTTP2Options].maxConcurrentStreams, 10)
+  await withWindow.close()
+
+  t.throws(() => new Client('https://localhost', {
+    h2Options: { maxConcurrentStreams: 'not-a-number', connectionWindowSize: 65535 }
+  }), { code: 'UND_ERR_INVALID_ARG' })
+
+  t.throws(() => new Client('https://localhost', {
+    h2Options: { maxConcurrentStreams: 0 }
+  }), { code: 'UND_ERR_INVALID_ARG' })
+})
+
+test('h2Options.settings.initialWindowSize reaches the session options', async (t) => {
+  t = tspl(t, { plan: 2 })
+
+  const client = new Client('https://localhost', {
+    h2Options: { settings: { initialWindowSize: 131072 } }
+  })
+  t.strictEqual(client[kHTTP2Options].sessionOptions.initialWindowSize, 131072)
+  await client.close()
+
+  const defaulted = new Client('https://localhost', { h2Options: {} })
+  t.strictEqual(defaulted[kHTTP2Options].sessionOptions.initialWindowSize, 262144)
+  await defaulted.close()
+})