diff --git a/miss_islington/tasks.py b/miss_islington/tasks.py
index 6f1cd745..89d1d6d9 100644
--- a/miss_islington/tasks.py
+++ b/miss_islington/tasks.py
@@ -1,4 +1,5 @@
 import asyncio
+import logging
 import os
 import ssl
 import subprocess
@@ -15,6 +16,7 @@
 
 from . import util
 
+logger = logging.getLogger(__name__)
 
 app = celery.Celery("backport_cpython")
 
@@ -116,16 +118,39 @@ async def backport_task_asyncio(
         # Ensure that we don't have any changes lying around
         subprocess.check_output(['git', 'reset', '--hard'])
         subprocess.check_output(['git', 'clean', '-fxd'])
-
-        cp = cherry_picker.CherryPicker(
-            "origin",
-            commit_hash,
-            [branch],
-            config=CHERRY_PICKER_CONFIG,
-            prefix_commit=False,
+        # Clear any leftover cherry-picker state from a previously interrupted
+        # run; otherwise CherryPicker() init raises InvalidRepoException and
+        # every subsequent backport on this worker silently fails.
+        subprocess.run(
+            ['git', 'config', '--local', '--remove-section', 'cherry-picker'],
+            stderr=subprocess.DEVNULL,
+            check=False,
         )
+
         try:
+            cp = cherry_picker.CherryPicker(
+                "origin",
+                commit_hash,
+                [branch],
+                config=CHERRY_PICKER_CONFIG,
+                prefix_commit=False,
+            )
             cp.backport()
+        except cherry_picker.InvalidRepoException as ire:
+            await util.comment_on_pr(
+                gh,
+                issue_number,
+                f"""\
+                Sorry {util.get_participants(created_by, merged_by)}, I had trouble backporting to `{branch}`.
+                Please retry by removing and re-adding the "needs backport to {branch}" label.
+                Alternatively, you can backport using [cherry_picker](https://pypi.org/project/cherry-picker/) on the command line.
+                ```
+                cherry_picker {commit_hash} {branch}
+                ```
+                """,
+            )
+            await util.assign_pr_to_core_dev(gh, issue_number, merged_by)
+            logger.exception("InvalidRepoException while backporting to %s", branch)
         except cherry_picker.BranchCheckoutException as bce:
             await util.comment_on_pr(
                 gh,
diff --git a/tests/test_tasks.py b/tests/test_tasks.py
new file mode 100644
index 00000000..ae7256fe
--- /dev/null
+++ b/tests/test_tasks.py
@@ -0,0 +1,60 @@
+import os
+import subprocess
+from unittest import mock
+
+from cherry_picker import cherry_picker
+
+os.environ.setdefault("HEROKU_REDIS_MAROON_URL", "someurl")
+
+from miss_islington import tasks
+
+
+async def test_invalid_repo_exception_posts_comment_and_clears_state():
+    """A stuck cherry-picker.state in git config used to wedge every
+    subsequent backport: CherryPicker() init raised InvalidRepoException
+    and the task crashed with no comment posted. The task now wipes
+    stale state pre-flight and posts an error comment if init still fails.
+    """
+    with (
+        mock.patch("miss_islington.tasks.aiohttp.ClientSession"),
+        mock.patch(
+            "miss_islington.tasks.apps.get_installation_access_token",
+            new=mock.AsyncMock(return_value={"token": "test-token"}),
+        ),
+        mock.patch("miss_islington.tasks.util.is_cpython_repo", return_value=True),
+        mock.patch("miss_islington.tasks.subprocess.check_output"),
+        mock.patch("miss_islington.tasks.subprocess.run") as run_mock,
+        mock.patch(
+            "miss_islington.tasks.cherry_picker.CherryPicker",
+            side_effect=cherry_picker.InvalidRepoException("stuck state"),
+        ),
+        mock.patch(
+            "miss_islington.tasks.util.comment_on_pr", new=mock.AsyncMock()
+        ) as comment_mock,
+        mock.patch(
+            "miss_islington.tasks.util.assign_pr_to_core_dev", new=mock.AsyncMock()
+        ) as assign_mock,
+    ):
+        await tasks.backport_task_asyncio(
+            "7a4c6dfb8839eb05fb87baf70364680e45001dd4",
+            "3.15",
+            issue_number=130749,
+            created_by="medmunds",
+            merged_by="bitdancer",
+            installation_id=42958231,
+        )
+
+    run_mock.assert_any_call(
+        ["git", "config", "--local", "--remove-section", "cherry-picker"],
+        stderr=subprocess.DEVNULL,
+        check=False,
+    )
+
+    comment_mock.assert_awaited_once()
+    posted_message = comment_mock.await_args.args[2]
+    assert "3.15" in posted_message
+    assert "@bitdancer" in posted_message
+
+    assign_mock.assert_awaited_once()
+    assert assign_mock.await_args.args[1] == 130749
+    assert assign_mock.await_args.args[2] == "bitdancer"