diff --git a/copyparty/__main__.py b/copyparty/__main__.py
index 63100cb5..e8c95884 100644
--- a/copyparty/__main__.py
+++ b/copyparty/__main__.py
@@ -1334,7 +1334,7 @@ def add_upload(ap):
     ap2.add_argument("--nrand", metavar="NUM", type=int, default=9, help="randomized filenames length (volflag=nrand)")
     ap2.add_argument("--magic", action="store_true", help="enable filetype detection on nameless uploads (volflag=magic)")
     ap2.add_argument("--df", metavar="GiB", type=u, default="0", help="ensure \033[33mGiB\033[0m free disk space by rejecting upload requests; assumes gigabytes unless a unit suffix is given: [\033[32m256m\033[0m], [\033[32m4\033[0m], [\033[32m2T\033[0m] (volflag=df)")
-    ap2.add_argument("--sparse", metavar="MiB", type=int, default=4, help="windows-only: minimum size of incoming uploads through up2k before they are made into sparse files")
+    ap2.add_argument("--sparse", metavar="MiB", type=int, default=1, help="windows-only: minimum size of incoming uploads through up2k before they are made into sparse files")
     ap2.add_argument("--turbo", metavar="LVL", type=int, default=0, help="configure turbo-mode in up2k client; [\033[32m-1\033[0m] = forbidden/always-off, [\033[32m0\033[0m] = default-off and warn if enabled, [\033[32m1\033[0m] = default-off, [\033[32m2\033[0m] = on, [\033[32m3\033[0m] = on and disable datecheck")
     ap2.add_argument("--nosubtle", metavar="N", type=int, default=0, help="when to use a wasm-hasher instead of the browser's builtin; faster on chrome, but buggy in older chrome versions. [\033[32m0\033[0m] = only when necessary (non-https), [\033[32m1\033[0m] = always (all browsers), [\033[32m2\033[0m] = always on chrome/firefox, [\033[32m3\033[0m] = always on chrome, [\033[32mN\033[0m] = chrome-version N and newer (recommendation: 137)")
     ap2.add_argument("--u2j", metavar="JOBS", type=int, default=2, help="web-client: number of file chunks to upload in parallel; 1 or 2 is good when latency is low (same-country), 2~4 for android-clients, 2~6 for cross-atlantic. Max is 6 in most browsers. Big values increase network-speed but may reduce HDD-speed")
diff --git a/copyparty/up2k.py b/copyparty/up2k.py
index 3027b1dc..bedfebd2 100644
--- a/copyparty/up2k.py
+++ b/copyparty/up2k.py
@@ -74,6 +74,7 @@ from .util import (
     vsplit,
     w8b64dec,
     w8b64enc,
+    winsparse,
     wunlink,
 )
 
@@ -5315,9 +5316,12 @@ class Up2k(object):
                 and self.args.sparse * 1024 * 1024 <= sz
             ):
                 try:
-                    sp.check_call(["fsutil", "sparse", "setflag", abspath])
-                except:
-                    self.log("could not sparse %r" % (abspath,), 3)
+                    winsparse(f)
+                    # some kernels/etc are buggy; force sync:
+                    f.close()
+                    f = open(abspath, "rb+")
+                except Exception as ex:
+                    self.log("could not sparse %r: %s" % (abspath, ex), 3)
                     relabel = True
                     sprs = False
 
diff --git a/copyparty/util.py b/copyparty/util.py
index e8fe6602..ebd69ffc 100644
--- a/copyparty/util.py
+++ b/copyparty/util.py
@@ -4523,6 +4523,18 @@ def hidedir(dp) -> None:
             pass
 
 
+def winsparse(f: typing.BinaryIO) -> None:
+    assert ctypes  # !rm
+    assert wk32  # !rm
+    import msvcrt
+
+    fh = msvcrt.get_osfhandle(f.fileno())
+    if not wk32.DeviceIoControl(
+        fh, 0x900C4, None, 0, None, 0, ctypes.byref(ctypes.c_ulong()), None
+    ):
+        raise ctypes.WinError(ctypes.get_last_error())
+
+
 _flocks = {}