diff --git a/src/calibre/srv/embedded.py b/src/calibre/srv/embedded.py
index ecabba3f62..2f3bfc9333 100644
--- a/src/calibre/srv/embedded.py
+++ b/src/calibre/srv/embedded.py
@@ -46,10 +46,6 @@ class Server(object):
         self.opts = opts
         self.log, self.access_log = log, access_log
         self.handler.set_log(self.log)
-        _df = os.environ.get('CALIBRE_DEVELOP_FROM', None)
-        if _df and os.path.exists(_df):
-            from calibre.utils.rapydscript import compile_srv
-            compile_srv()
 
     @property
     def user_manager(self):
@@ -91,6 +87,10 @@ class Server(object):
                 pass
         reset_caches()  # we reset the cache as the server tdir has changed
         try:
+            _df = os.environ.get('CALIBRE_DEVELOP_FROM', None)
+            if _df and os.path.exists(_df):
+                from calibre.utils.rapydscript import compile_srv
+                compile_srv()
             self.loop.serve_forever()
         except BaseException as e:
             self.exception = e
diff --git a/src/calibre/utils/rapydscript.py b/src/calibre/utils/rapydscript.py
index 61c9405d6c..799e1126e6 100644
--- a/src/calibre/utils/rapydscript.py
+++ b/src/calibre/utils/rapydscript.py
@@ -19,6 +19,7 @@ from threading import Thread, local
 
 from calibre import force_unicode
 from calibre.constants import __appname__, __version__, cache_dir
+from calibre.utils.filenames import atomic_rename
 from calibre.utils.terminal import ANSIStream
 from duktape import Context, JSError, to_python
 from lzma.xz import compress, decompress
@@ -223,10 +224,16 @@ def compile_srv():
         html = f.read().replace(b'RESET_STYLES', reset, 1).replace(b'ICONS', icons, 1).replace(b'MAIN_JS', js, 1)
 
     manifest = create_manifest(html)
-    with lopen(os.path.join(base, 'index-generated.html'), 'wb') as f:
-        f.write(html)
-    with lopen(os.path.join(base, 'calibre.appcache'), 'wb') as f:
-        f.write(manifest)
+
+    def atomic_write(name, content):
+        name = os.path.join(base, name)
+        tname = name + '.tmp'
+        with lopen(tname, 'wb') as f:
+            f.write(content)
+        atomic_rename(tname, name)
+
+    atomic_write('index-generated.html', html)
+    atomic_write('calibre.appcache', manifest)
 
 # }}}