diff --git a/src/pyj/ajax.pyj b/src/pyj/ajax.pyj
index 6321ffa696..2701e02e95 100644
--- a/src/pyj/ajax.pyj
+++ b/src/pyj/ajax.pyj
@@ -4,6 +4,14 @@
 from gettext import gettext as _
 
 def ajax(path, on_complete, on_progress=None, bypass_cache=True, method='GET', query=None, timeout=30*1000, ok_code=200):
+    # Run an AJAX request. on_complete must be a function that accepts three
+    # arguments: end_type, xhr, ev where end_type is one of 'abort', 'error',
+    # 'load', 'timeout'. In case end_type is anything other than 'load' you can
+    # get a descriptive error message via `xhr.error_html`.  on_progress, if
+    # provided must be a function accepting three arguments: loaded, total, xhr
+    # where loaded is the number of bytes received, total is the total size.
+    #
+    # Returns the xhr object, call xhr.send() to start the request.
     query = query or {}
     xhr = XMLHttpRequest()
     keys = Object.keys(query)
@@ -19,16 +27,16 @@ def ajax(path, on_complete, on_progress=None, bypass_cache=True, method='GET', q
         path += ('&' if has_query else '?') + Date().getTime()
 
     xhr.request_path = path
-    xhr.error_string = ''
+    xhr.error_html = ''
 
     def set_error(event):
         if event == 'timeout':
-            xhr.error_string = str.format(_('Failed to communicate with "{}", timed out after: {} seconds'), xhr.request_path, timeout/1000)
+            xhr.error_html = str.format(_('Failed to communicate with "{}", timed out after: {} seconds'), xhr.request_path, timeout/1000)
         elif event == 'abort':
-            xhr.error_string = str.format(_('Failed to communicate with "{}", aborted'), xhr.request_path)
+            xhr.error_html = str.format(_('Failed to communicate with "{}", aborted'), xhr.request_path)
         else:
             rtext = xhr.responseText or ''
-            xhr.error_string = str.format(_('Failed to communicate with "{}", with status: [{}] {}<br>{}'), xhr.request_path, xhr.status, xhr.statusText, rtext[:200])
+            xhr.error_html = str.format(_('Failed to communicate with "{}", with status: [{}] {}<br>{}'), xhr.request_path, xhr.status, xhr.statusText, rtext[:200])
 
     def progress_callback(ev):
         if ev.lengthComputable:
@@ -40,7 +48,7 @@ def ajax(path, on_complete, on_progress=None, bypass_cache=True, method='GET', q
                     ul = int(ul)
                 except Exception:
                     return
-                on_progress(ev.loaded, ul)
+                on_progress(ev.loaded, ul, xhr)
 
     def complete_callback(end_type, ev):
         if xhr.status != ok_code and end_type == 'load':
diff --git a/src/pyj/modals.pyj b/src/pyj/modals.pyj
index 44d46afdb9..c9a90e1346 100644
--- a/src/pyj/modals.pyj
+++ b/src/pyj/modals.pyj
@@ -1,6 +1,7 @@
 # vim:fileencoding=utf-8
 # License: GPL v3 Copyright: 2015, Kovid Goyal <kovid at kovidgoyal.net>
 
+from ajax import ajax
 from elementmaker import E
 from dom import set_css, clear, build_rule
 from gettext import gettext as _
@@ -162,7 +163,7 @@ def create_progress_dialog(msg, on_close):
 
 # def test_progress():
 #     counter = 0
-#     pd = progress_dialog('Testing progress dialog', def():
+#     pd = progress_dialog('Testing progress dialog, please wait...', def():
 #         nonlocal counter
 #         counter = 101
 #         console.log('pd canceled')
@@ -203,4 +204,23 @@ def warning_dialog(title, msg, details=None):
     create_simple_dialog(title, msg, details, 'warning', _('Warning:'))
 
 def progress_dialog(msg, on_close=None):
+    # Show a modal dialog with a progress bar and an optional close button.
+    # If the user clicks the close button, on_close is called and the dialog is closed.
+    # Returns an object with the methods: close(), update_progress(amount, total), set_msg()
+    # Call update_progress() to update the progress bar
+    # Call set_msg() to change the displayed message
+    # Call close() once the task being performed is finished
     return create_progress_dialog(msg, on_close)
+
+def ajax_progress_dialog(path, on_complete, msg, **kw):
+    pd = None
+    def on_complete_callback(event_type, xhr, ev):
+        nonlocal pd
+        pd.close()
+        pd = undefined
+        return on_complete(event_type, xhr, ev)
+    def on_progress_callback(loaded, total, xhr):
+        pd.update_progress(loaded, total)
+    xhr = ajax(path, on_complete_callback, on_progress=on_progress_callback, **kw)
+    pd = progress_dialog(msg, xhr.abort)
+    return xhr, pd