diff --git a/.hgignore b/.hgignore
index 174084f832..f86bd0f243 100644
--- a/.hgignore
+++ b/.hgignore
@@ -63,6 +63,7 @@ locale/*/LC_MESSAGES/hg.mo
 hgext/__index__.py
 hgext/clindex.c
 hgext/extlib/linelog.c
+hgext/patchrmdir.c
 hgext/traceprof.cpp
 
 # Rust libraries and extensions
diff --git a/fb-hgext/hgext3rd/patchrmdir.pyx b/fb-hgext/hgext3rd/patchrmdir.pyx
deleted file mode 100644
index 3f70ff6937..0000000000
--- a/fb-hgext/hgext3rd/patchrmdir.pyx
+++ /dev/null
@@ -1,63 +0,0 @@
-# patchrmdir.py
-#
-# Copyright 2017 Facebook, Inc.
-#
-# This software may be used and distributed according to the terms of the
-# GNU General Public License version 2 or any later version.
-
-"""patch rmdir
-
-Check if a directory is empty before trying to call rmdir on it. This works
-around some kernel issues.
-"""
-
-from mercurial import (
-    extensions,
-)
-import os
-import errno
-
-cdef extern from "dirent.h":
-    ctypedef struct DIR
-    struct dirent:
-        pass
-
-    DIR *opendir(const char *)
-    dirent *readdir(DIR *)
-    int closedir(DIR *)
-
-cdef int _countdir(const char *path):
-    """return min(3, the number of entries inside a directory).
-    return -1 if the directory cannot be opened.
-    """
-    cdef DIR *d = opendir(path)
-    if d == NULL:
-        return -1
-
-    cdef dirent *e
-    cdef int n = 0
-    while True:
-        e = readdir(d)
-        if e == NULL:
-            break
-        else:
-            n += 1
-            if n > 2:
-                break
-    closedir(d)
-    return n
-
-def _rmdir(orig, path):
-    n = _countdir(path)
-    if n >= 3:
-        # The number 3 is because most systems have "." and "..". For systems
-        # without them, we fallback to the original rmdir, the behavior should
-        # still be correct.
-        # Choose a slightly different error message other than "Directory not
-        # empty" so the test could notice the difference.
-        raise OSError(errno.ENOTEMPTY, 'Non-empty directory: %r' % path)
-    else:
-        return orig(path)
-
-def uisetup(ui):
-    extensions.wrapfunction(os, 'rmdir', _rmdir)
diff --git a/hgext/patchrmdir.pyx b/hgext/patchrmdir.pyx
new file mode 100644
index 0000000000..e644440df4
--- /dev/null
+++ b/hgext/patchrmdir.pyx
@@ -0,0 +1,67 @@
+# patchrmdir.py
+#
+# Copyright 2017 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+"""patch rmdir
+
+Check if a directory is empty before trying to call rmdir on it. This works
+around some kernel issues.
+
+Have no effect on Windows.
+"""
+
+IF UNAME_SYSNAME != "Windows":
+    from mercurial import (
+        extensions,
+        pycompat,
+    )
+    import os
+    import errno
+
+    cdef extern from "dirent.h":
+        ctypedef struct DIR
+        struct dirent:
+            pass
+
+        DIR *opendir(const char *)
+        dirent *readdir(DIR *)
+        int closedir(DIR *)
+
+    cdef int _countdir(const char *path):
+        """return min(3, the number of entries inside a directory).
+        return -1 if the directory cannot be opened.
+        """
+        cdef DIR *d = opendir(path)
+        if d == NULL:
+            return -1
+
+        cdef dirent *e
+        cdef int n = 0
+        while True:
+            e = readdir(d)
+            if e == NULL:
+                break
+            else:
+                n += 1
+                if n > 2:
+                    break
+        closedir(d)
+        return n
+
+    def _rmdir(orig, path):
+        n = _countdir(path)
+        if n >= 3:
+            # The number 3 is because most systems have "." and "..". For systems
+            # without them, we fallback to the original rmdir, the behavior should
+            # still be correct.
+            # Choose a slightly different error message other than "Directory not
+            # empty" so the test could notice the difference.
+            raise OSError(errno.ENOTEMPTY, 'Non-empty directory: %r' % path)
+        else:
+            return orig(path)
+
+    def uisetup(ui):
+        extensions.wrapfunction(os, 'rmdir', _rmdir)
diff --git a/setup.py b/setup.py
index 3279c8d5d1..1af8d7c8fc 100644
--- a/setup.py
+++ b/setup.py
@@ -1055,6 +1055,9 @@ extmodules += cythonize([
     Extension('hgext.clindex',
               sources=['hgext/clindex.pyx'],
               extra_compile_args=filter(None, [STDC99, PRODUCEDEBUGSYMBOLS])),
+    Extension('hgext.patchrmdir',
+              sources=['hgext/patchrmdir.pyx'],
+              extra_compile_args=filter(None, [PRODUCEDEBUGSYMBOLS])),
     Extension('hgext.traceprof',
               sources=['hgext/traceprof.pyx'],
               include_dirs=['hgext'],