diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 028a7861f36798..e0778000b1c817 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -648,8 +648,11 @@ functions.
    .. note::
 
       If specified, *env* must provide any variables required for the program to
-      execute.  On Windows, in order to run a `side-by-side assembly`_ the
-      specified *env* **must** include a valid :envvar:`SystemRoot`.
+      execute.  On Windows, in order to run a `side-by-side assembly`_, or a
+      Python program using the :mod:`socket` module (or another module that
+      depends on it, such as :mod:`asyncio`), the specified *env* **must**
+      include a valid :envvar:`!SystemRoot`; omitting it may emit a
+      :exc:`RuntimeWarning`.
 
    .. _side-by-side assembly: https://en.wikipedia.org/wiki/Side-by-Side_Assembly
 
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 54c2eb515b60da..1fcf8d8f224bdc 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1545,6 +1545,10 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
             if cwd is not None:
                 cwd = os.fsdecode(cwd)
 
+            if env is not None and not any(
+                    k.upper() == 'SYSTEMROOT' and v for k, v in env.items()):
+                warnings.warn("env lacks a valid 'SystemRoot'.", RuntimeWarning)
+
             sys.audit("subprocess.Popen", executable, args, cwd, env)
 
             # Start the process
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index ca35804fb36076..f94fe1e0dab60b 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -857,13 +857,14 @@ def test_one_environment_variable(self):
                                'sys.stdout.write("fruit="+os.getenv("fruit"))']
         if sys.platform == "win32":
             cmd = ["CMD", "/c", "SET", "fruit"]
-        with subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=newenv) as p:
-            stdout, stderr = p.communicate()
-            if p.returncode and support.verbose:
-                print("STDOUT:", stdout.decode("ascii", "replace"))
-                print("STDERR:", stderr.decode("ascii", "replace"))
-            self.assertEqual(p.returncode, 0)
-            self.assertEqual(stdout.strip(), b"fruit=orange")
+        with warnings_helper.check_warnings(('env.*SystemRoot', RuntimeWarning), quiet=True):
+            with subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=newenv) as p:
+                stdout, stderr = p.communicate()
+                if p.returncode and support.verbose:
+                    print("STDOUT:", stdout.decode("ascii", "replace"))
+                    print("STDERR:", stderr.decode("ascii", "replace"))
+                self.assertEqual(p.returncode, 0)
+                self.assertEqual(stdout.strip(), b"fruit=orange")
 
     def test_invalid_cmd(self):
         # null character in the command name
@@ -1764,7 +1765,8 @@ def test_run_with_an_empty_env(self):
         args = [sys.executable, "-c", 'pass']
         # Ignore subprocess errors - we only care that the API doesn't
         # raise an OSError
-        subprocess.run(args, env={})
+        with warnings_helper.check_warnings(('env.*SystemRoot', RuntimeWarning), quiet=True):
+            subprocess.run(args, env={})
 
     def test_capture_output(self):
         cp = self.run_python(("import sys;"
@@ -3567,7 +3569,8 @@ def test_issue31471(self):
         class BadEnv(dict):
             keys = None
         with self.assertRaises(TypeError):
-            subprocess.Popen(ZERO_RETURN_CMD, env=BadEnv())
+            with warnings_helper.check_warnings(('env.*SystemRoot', RuntimeWarning), quiet=True):
+                subprocess.Popen(ZERO_RETURN_CMD, env=BadEnv())
 
     def test_close_fds(self):
         # close file descriptors
diff --git a/Misc/NEWS.d/next/Windows/2025-05-21-10-48-38.gh-issue-118234.x1N6xT.rst b/Misc/NEWS.d/next/Windows/2025-05-21-10-48-38.gh-issue-118234.x1N6xT.rst
new file mode 100644
index 00000000000000..241be957c57d13
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2025-05-21-10-48-38.gh-issue-118234.x1N6xT.rst
@@ -0,0 +1,4 @@
+Document that :envvar:`!SystemRoot` is also required for a Python subprocess
+that uses :mod:`socket` or :mod:`asyncio` on Windows, and add a
+:exc:`RuntimeWarning` if an *env* supplied to :class:`subprocess.Popen`
+lacks it. Patch by John Keith Hohm.