diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 2044d2a42897e9..28edfc1de5b079 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1921,12 +1921,13 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
 
                 # Wait for exec to fail or succeed; possibly raising an
                 # exception (limited in size)
-                errpipe_data = bytearray()
-                while True:
-                    part = os.read(errpipe_read, 50000)
-                    errpipe_data += part
-                    if not part or len(errpipe_data) > 50000:
-                        break
+                errpipe_data = bytearray(50000)
+                unread = memoryview(errpipe_data)
+                while count := os.readinto(errpipe_read, unread):
+                    unread = unread[count:]
+                bytes_left = len(unread)
+                del unread
+                del errpipe_data[-bytes_left:]
             finally:
                 # be sure the FD is closed no matter what
                 os.close(errpipe_read)
diff --git a/Misc/NEWS.d/next/Library/2025-02-02-20-55-18.gh-issue-129205.hb1iMy.rst b/Misc/NEWS.d/next/Library/2025-02-02-20-55-18.gh-issue-129205.hb1iMy.rst
new file mode 100644
index 00000000000000..70e028a7c7fa38
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-02-02-20-55-18.gh-issue-129205.hb1iMy.rst
@@ -0,0 +1 @@
+:mod:`subprocess` forkserver now uses a fixed 50,000 byte buffer to read startup errors from the child processes it runs. Previously there could be up to 100,000 bytes read with multiple allocations and copies.