diff --git a/server/buildoutls/md5sum.py b/server/buildoutls/md5sum.py
index 410e332..95b1519 100644
--- a/server/buildoutls/md5sum.py
+++ b/server/buildoutls/md5sum.py
@@ -33,7 +33,7 @@ async def update_md5sum(
   ls.progress.begin(
       token,
       WorkDoneProgressBegin(
-          cancellable=True,  # TODO actually support cancellation
+          cancellable=True,
           title=f"Updating md5sum for {url}",
       ))
 
@@ -64,6 +64,8 @@ async def update_md5sum(
               message=f"{percentage:0.2f}% in {elapsed_time:0.2f}s",
               percentage=max(0, int(percentage)),
           ))
+      if ls.progress.tokens[token].cancelled():
+        break
 
   hexdigest = m.hexdigest()
 
@@ -88,13 +90,14 @@ async def update_md5sum(
     )
     new_text = f"md5sum = {hexdigest}\n"
 
-  ls.progress.end(token, WorkDoneProgressEnd())
-  ls.apply_edit(
-      WorkspaceEdit(
-          changes={
-              md5sum_location.uri:
-              [TextEdit(
-                  range=md5sum_location.range,
-                  new_text=new_text,
-              )]
-          }))
+  if not ls.progress.tokens[token].cancelled():
+    ls.progress.end(token, WorkDoneProgressEnd())
+    ls.apply_edit(
+        WorkspaceEdit(
+            changes={
+                md5sum_location.uri:
+                [TextEdit(
+                    range=md5sum_location.range,
+                    new_text=new_text,
+                )]
+            }))
diff --git a/server/buildoutls/tests/conftest.py b/server/buildoutls/tests/conftest.py
index 0490ef5..4ad54f3 100644
--- a/server/buildoutls/tests/conftest.py
+++ b/server/buildoutls/tests/conftest.py
@@ -1,3 +1,5 @@
+import collections
+import concurrent.futures
 import os
 import urllib.parse
 from typing import Any
@@ -55,6 +57,7 @@ def __init__(self):
     show_message_log = mock.Mock()
     apply_edit = mock.Mock()
     progress = mock.create_autospec(pygls.progress.Progress)
+    progress.tokens = collections.defaultdict(concurrent.futures.Future)
 
   server = FakeServer()
 
diff --git a/server/buildoutls/tests/test_code_actions.py b/server/buildoutls/tests/test_code_actions.py
index ac44ada..d905395 100644
--- a/server/buildoutls/tests/test_code_actions.py
+++ b/server/buildoutls/tests/test_code_actions.py
@@ -1,3 +1,5 @@
+import collections
+import concurrent.futures
 import json
 import pathlib
 import textwrap
@@ -550,6 +552,55 @@ async def test_update_md5sum_code_action_without_md5sum_option(
       }, ), )
 
 
+async def test_update_md5sum_code_action_cancelled(
+    server,
+    example_com_response,
+) -> None:
+
+  code_action_params = CodeActionParams(
+      text_document=TextDocumentIdentifier(
+          uri='file:///code_actions/update_md5sum.cfg'),
+      range=Range(start=Position(line=1, character=11),
+                  end=Position(line=1, character=12)),
+      context=CodeActionContext(diagnostics=[]))
+
+  code_actions = await lsp_code_action(
+      server,
+      _dump_and_load(code_action_params),
+  )
+  assert isinstance(code_actions, list)
+  assert code_actions == [
+      CodeAction(
+          title='Update md5sum',
+          kind=CodeActionKind.QuickFix,
+          command=Command(
+              title='Update md5sum',
+              command=COMMAND_UPDATE_MD5SUM,
+              arguments=[
+                  UpdateMD5SumCommandParams(
+                      document_uri='file:///code_actions/update_md5sum.cfg',
+                      section_name='section',
+                  ),
+              ],
+          ),
+      )
+  ]
+  assert isinstance(code_actions[0].command, Command)
+  assert code_actions[0].command.arguments
+
+  def cancelled_future() -> concurrent.futures.Future[None]:
+    f: concurrent.futures.Future[None] = concurrent.futures.Future()
+    f.cancel()
+    return f
+
+  server.progress.tokens = collections.defaultdict(cancelled_future)
+
+  await command_update_md5sum(
+      server,
+      cast(List[UpdateMD5SumCommandParams], code_actions[0].command.arguments))
+  server.apply_edit.assert_not_called()
+
+
 @pytest.mark.parametrize(
     'range_',
     [