diff --git a/.changeset/fix-default-inherited-env-vars-windows.md b/.changeset/fix-default-inherited-env-vars-windows.md
new file mode 100644
index 0000000000..0f398e2e36
--- /dev/null
+++ b/.changeset/fix-default-inherited-env-vars-windows.md
@@ -0,0 +1,8 @@
+---
+'@modelcontextprotocol/sdk': patch
+---
+
+On Windows, stdio servers spawned by `StdioClientTransport` now also inherit `COMSPEC`, `PATHEXT`, `PROGRAMDATA`, `PROGRAMFILES(X86)`, `PROGRAMW6432`, and `WINDIR` (added to `DEFAULT_INHERITED_ENV_VARS`). Programs a server launches can depend on them: PowerShell finds no native
+executables without `PATHEXT`, and Windows OpenSSH exits 255 without `ProgramData`.
+
+This is a backport of the same fix already merged on `main` in #2043, and resolves #2037 for the v1 line.
diff --git a/src/client/stdio.ts b/src/client/stdio.ts
index 816a686fce..b30578c4a4 100644
--- a/src/client/stdio.ts
+++ b/src/client/stdio.ts
@@ -54,17 +54,23 @@ export const DEFAULT_INHERITED_ENV_VARS =
     process.platform === 'win32'
         ? [
               'APPDATA',
+              'COMSPEC',
               'HOMEDRIVE',
               'HOMEPATH',
               'LOCALAPPDATA',
               'PATH',
+              'PATHEXT',
               'PROCESSOR_ARCHITECTURE',
+              'PROGRAMDATA',
+              'PROGRAMFILES',
+              'PROGRAMFILES(X86)',
+              'PROGRAMW6432',
               'SYSTEMDRIVE',
               'SYSTEMROOT',
               'TEMP',
               'USERNAME',
               'USERPROFILE',
-              'PROGRAMFILES'
+              'WINDIR'
           ]
         : /* list inspired by the default env inheritance of sudo */
           ['HOME', 'LOGNAME', 'PATH', 'SHELL', 'TERM', 'USER'];
diff --git a/test/client/stdio.test.ts b/test/client/stdio.test.ts
index 577e0c946f..f7ff8ab3ff 100644
--- a/test/client/stdio.test.ts
+++ b/test/client/stdio.test.ts
@@ -116,3 +116,36 @@ test('should fire onerror and close when ReadBuffer overflows', async () => {
     expect(error.message).toMatch(/ReadBuffer exceeded maximum size/);
     await closed;
 });
+
+test('should inherit the Windows variables that child tools need by default', async () => {
+    const originalPlatform = process.platform;
+    // DEFAULT_INHERITED_ENV_VARS is computed at import time, so load a fresh copy of the module as if on Windows.
+    Object.defineProperty(process, 'platform', { value: 'win32' });
+    try {
+        vi.resetModules();
+        const { DEFAULT_INHERITED_ENV_VARS } = await import('../../src/client/stdio.js');
+        expect(DEFAULT_INHERITED_ENV_VARS).toEqual([
+            'APPDATA',
+            'COMSPEC',
+            'HOMEDRIVE',
+            'HOMEPATH',
+            'LOCALAPPDATA',
+            'PATH',
+            'PATHEXT',
+            'PROCESSOR_ARCHITECTURE',
+            'PROGRAMDATA',
+            'PROGRAMFILES',
+            'PROGRAMFILES(X86)',
+            'PROGRAMW6432',
+            'SYSTEMDRIVE',
+            'SYSTEMROOT',
+            'TEMP',
+            'USERNAME',
+            'USERPROFILE',
+            'WINDIR'
+        ]);
+    } finally {
+        Object.defineProperty(process, 'platform', { value: originalPlatform });
+        vi.resetModules();
+    }
+});