diff --git a/bedevere/util.py b/bedevere/util.py
index a18250a9..97dddffe 100644
--- a/bedevere/util.py
+++ b/bedevere/util.py
@@ -3,7 +3,18 @@
 
 import gidgethub
 
+
+DEFAULT_BODY = ""
+TAG_NAME = "gh-issue-number"
 NEWS_NEXT_DIR = "Misc/NEWS.d/next/"
+CLOSING_TAG = f"<!-- /{TAG_NAME} -->"
+BODY = f"""\
+{{body}}
+
+<!-- {TAG_NAME}: gh-{{issue_number}} -->
+* gh-{{issue_number}}
+{CLOSING_TAG}
+"""
 
 
 @enum.unique
@@ -67,7 +78,10 @@ async def files_for_PR(gh, pull_request):
     data = []
     async for filedata in gh.getiter(files_url):  # pragma: no branch
         data.append(
-            {"file_name": filedata["filename"], "patch": filedata.get("patch", ""),}
+            {
+                "file_name": filedata["filename"],
+                "patch": filedata.get("patch", ""),
+            }
         )
     return data
 
@@ -77,6 +91,24 @@ async def issue_for_PR(gh, pull_request):
     return await gh.getitem(pull_request["issue_url"])
 
 
+async def patch_body(gh, pull_request, issue_number):
+    """Updates the description of a PR with the gh issue number if it exists.
+
+    returns if body exists with issue_number
+    """
+    if "body" not in pull_request or pull_request["body"] is None:
+        return await gh.patch(
+            pull_request["url"],
+            data=BODY.format(body=DEFAULT_BODY, issue_number=issue_number),
+        )
+    if f"GH-{issue_number}\n" not in pull_request["body"]:
+        return await gh.patch(
+            pull_request["url"],
+            data=BODY.format(body=pull_request["body"], issue_number=issue_number),
+        )
+    return
+
+
 async def is_core_dev(gh, username):
     """Check if the user is a CPython core developer."""
     org_teams = "/orgs/python/teams"
diff --git a/tests/test_gh_issue.py b/tests/test_gh_issue.py
index 8a47d6c2..729bc258 100644
--- a/tests/test_gh_issue.py
+++ b/tests/test_gh_issue.py
@@ -12,11 +12,14 @@
 
 class FakeGH:
 
-    def __init__(self, *, getitem=None, post=None):
+    def __init__(self, *, getitem=None, post=None, patch=None):
         self._getitem_return = getitem
         self._post_return = post
+        self._patch_return = patch
         self.post_url = []
         self.post_data = []
+        self.patch_url = []
+        self.patch_data = []
 
     async def getitem(self, url):
         if isinstance(self._getitem_return, Exception):
@@ -28,7 +31,6 @@ async def post(self, url, *, data):
         self.post_data.append(data)
         return self._post_return
 
-
 @pytest.mark.asyncio
 @pytest.mark.parametrize("action", ["opened", "synchronize", "reopened"])
 async def test_set_status_failure(action, monkeypatch):
@@ -40,6 +42,7 @@ async def test_set_status_failure(action, monkeypatch):
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "No issue in title",
             "issue_url": "issue URL",
+            "url": "url",
         },
     }
     issue_data = {
@@ -68,6 +71,8 @@ async def test_set_status_failure_via_issue_not_found_on_github(action, monkeypa
         "pull_request": {
              "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "gh-123: Invalid issue number",
+            "issue_url": "issue URL",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -88,7 +93,9 @@ async def test_set_status_success_issue_found_on_bpo(action):
         "action": action,
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
-            "title": "bpo-12345: an issue!",
+            "title": "bpo-12345: An issue on b.p.o",
+            "issue_url": "issue URL",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -112,6 +119,7 @@ async def test_set_status_success(action, monkeypatch):
         "action": action,
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
+            "url": "",
             "title": "[3.6] gh-1234: an issue!",
         },
     }
@@ -137,6 +145,7 @@ async def test_set_status_success_issue_found_on_gh(action, monkeypatch):
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "gh-12345: an issue!",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -161,6 +170,7 @@ async def test_set_status_success_issue_found_on_gh_ignore_case(action, monkeypa
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "GH-12345: an issue!",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -186,6 +196,7 @@ async def test_set_status_success_via_skip_issue_label(action, monkeypatch):
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "No issue in title",
             "issue_url": "issue URL",
+            "url": "url",
         },
     }
     issue_data = {
@@ -211,6 +222,7 @@ async def test_edit_title(monkeypatch):
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "gh-1234: an issue!",
+            "url": "url",
         },
         "action": "edited",
         "changes": {"title": "thingy"},
@@ -251,6 +263,7 @@ async def test_edit_other_than_title(monkeypatch):
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "bpo-1234: an issue!",
+            "url": "url",
         },
         "action": "edited",
         "changes": {"stuff": "thingy"},
@@ -270,6 +283,7 @@ async def test_new_label_skip_issue_no_issue():
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "An easy fix",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -287,6 +301,7 @@ async def test_new_label_skip_issue_with_issue_number():
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "Revert gh-1234: revert an easy fix",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -308,6 +323,7 @@ async def test_new_label_skip_issue_with_issue_number_ignore_case():
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "Revert Gh-1234: revert an easy fix",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -327,6 +343,7 @@ async def test_new_label_not_skip_issue():
         "label": {"name": "non-trivial"},
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -347,6 +364,7 @@ async def test_removed_label_from_label_deletion(monkeypatch):
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "gh-1234: an issue!",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -366,6 +384,7 @@ async def test_removed_label_skip_issue(monkeypatch):
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
             "title": "gh-1234: an issue!",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -389,6 +408,7 @@ async def test_removed_label_non_skip_issue(monkeypatch):
         "label": {"name": "non-trivial"},
         "pull_request": {
             "statuses_url": "https://api.github.com/blah/blah/git-sha",
+            "url": "url",
         },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
@@ -422,7 +442,7 @@ async def test_validate_issue_number_is_pr_on_github():
 
     gh = FakeGH(getitem={
         "number": 123,
-        "pull_request": {"html_url": "https://github.com/python/cpython/pull/123"}
+        "pull_request": {"html_url": "https://github.com/python/cpython/pull/123", "url": "url",}
     })
     async with aiohttp.ClientSession() as session:
         response = await gh_issue._validate_issue_number(gh, 123, session=session)
diff --git a/tests/test_stage.py b/tests/test_stage.py
index af450001..fd9bb814 100644
--- a/tests/test_stage.py
+++ b/tests/test_stage.py
@@ -18,6 +18,7 @@ def __init__(self, *, getiter=None, getitem=None, delete=None, post=None):
         self.getitem_url = None
         self.delete_url = None
         self.post_ = []
+        self.patch_ = []
 
     async def getiter(self, url, url_vars={}):
         self.getiter_url = sansio.format_url(url, url_vars)
@@ -40,6 +41,10 @@ async def post(self, url, url_vars={}, *, data):
         post_url = sansio.format_url(url, url_vars)
         self.post_.append((post_url, data))
 
+    async def patch(self, url, url_vars={}, *, data):
+        patch_url = sansio.format_url(url, url_vars)
+        self.patch_.append((patch_url, data))
+
 
 async def test_stage():
     # Skip changing labels if the label is already set.
@@ -73,7 +78,12 @@ async def test_opened_pr():
     issue_url = "https://api.github.com/issue/42"
     data = {
         "action": "opened",
-        "pull_request": {"user": {"login": username,}, "issue_url": issue_url,},
+        "pull_request": {
+            "user": {
+                "login": username,
+            },
+            "issue_url": issue_url,
+        },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
     teams = [{"name": "python core", "id": 6}]
@@ -95,7 +105,12 @@ async def test_opened_pr():
     issue_url = "https://api.github.com/issue/42"
     data = {
         "action": "opened",
-        "pull_request": {"user": {"login": username,}, "issue_url": issue_url,},
+        "pull_request": {
+            "user": {
+                "login": username,
+            },
+            "issue_url": issue_url,
+        },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
     teams = [{"name": "python core", "id": 6}]
@@ -120,7 +135,12 @@ async def test_new_review():
     username = "andreamcinnes"
     data = {
         "action": "submitted",
-        "review": {"state": "approved", "user": {"login": username,},},
+        "review": {
+            "state": "approved",
+            "user": {
+                "login": username,
+            },
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -176,7 +196,12 @@ async def test_new_review():
     # First comment review from a non-core dev.
     data = {
         "action": "submitted",
-        "review": {"state": "comment", "user": {"login": username,},},
+        "review": {
+            "state": "comment",
+            "user": {
+                "login": username,
+            },
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -208,7 +233,12 @@ async def test_new_review():
     username = "brettcannon"
     data = {
         "action": "submitted",
-        "review": {"user": {"login": username,}, "state": "APPROVED",},
+        "review": {
+            "user": {
+                "login": username,
+            },
+            "state": "APPROVED",
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -239,7 +269,12 @@ async def test_new_review():
     username = "brettcannon"
     data = {
         "action": "submitted",
-        "review": {"user": {"login": username,}, "state": "APPROVED",},
+        "review": {
+            "user": {
+                "login": username,
+            },
+            "state": "APPROVED",
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -266,7 +301,12 @@ async def test_new_review():
     # Core dev requests changes.
     data = {
         "action": "submitted",
-        "review": {"user": {"login": username,}, "state": "changes_requested".upper(),},
+        "review": {
+            "user": {
+                "login": username,
+            },
+            "state": "changes_requested".upper(),
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -299,7 +339,12 @@ async def test_new_review():
     # Comment reviews do nothing.
     data = {
         "action": "submitted",
-        "review": {"user": {"login": username,}, "state": "commented".upper(),},
+        "review": {
+            "user": {
+                "login": username,
+            },
+            "state": "commented".upper(),
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -315,7 +360,12 @@ async def test_new_review():
     # Skip commenting if "awaiting changes" is already set.
     data = {
         "action": "submitted",
-        "review": {"user": {"login": username,}, "state": "changes_requested".upper(),},
+        "review": {
+            "user": {
+                "login": username,
+            },
+            "state": "changes_requested".upper(),
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -354,7 +404,12 @@ async def test_non_core_dev_does_not_downgrade():
     # Approval from a core dev changes the state to "Awaiting merge".
     data = {
         "action": "submitted",
-        "review": {"state": "approved", "user": {"login": core_dev,},},
+        "review": {
+            "state": "approved",
+            "user": {
+                "login": core_dev,
+            },
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -378,7 +433,12 @@ async def test_non_core_dev_does_not_downgrade():
     # Non-comment review from a non-core dev doesn't "downgrade" the PR's state.
     data = {
         "action": "submitted",
-        "review": {"state": "approved", "user": {"login": non_core_dev,},},
+        "review": {
+            "state": "approved",
+            "user": {
+                "login": non_core_dev,
+            },
+        },
         "pull_request": {
             "url": "https://api.github.com/pr/42",
             "issue_url": "https://api.github.com/issue/42",
@@ -515,7 +575,9 @@ async def test_change_requested_for_core_dev():
     data = {
         "action": "submitted",
         "review": {
-            "user": {"login": "gvanrossum",},
+            "user": {
+                "login": "gvanrossum",
+            },
             "state": "changes_requested".upper(),
         },
         "pull_request": {
@@ -561,7 +623,9 @@ async def test_change_requested_for_non_core_dev():
     data = {
         "action": "submitted",
         "review": {
-            "user": {"login": "gvanrossum",},
+            "user": {
+                "login": "gvanrossum",
+            },
             "state": "changes_requested".upper(),
         },
         "pull_request": {
@@ -621,7 +685,10 @@ async def test_awaiting_label_removed_when_pr_merged(label):
     issue_url = "https://api.github.com/repos/org/proj/issues/3749"
     data = {
         "action": "closed",
-        "pull_request": {"merged": True, "issue_url": issue_url,},
+        "pull_request": {
+            "merged": True,
+            "issue_url": issue_url,
+        },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
 
@@ -657,7 +724,10 @@ async def test_awaiting_label_not_removed_when_pr_not_merged(label):
     issue_url = "https://api.github.com/repos/org/proj/issues/3749"
     data = {
         "action": "closed",
-        "pull_request": {"merged": False, "issue_url": issue_url,},
+        "pull_request": {
+            "merged": False,
+            "issue_url": issue_url,
+        },
     }
     event = sansio.Event(data, event="pull_request", delivery_id="12345")
 
@@ -699,7 +769,14 @@ async def test_new_commit_pushed_to_approved_pr():
                     "number": 5547,
                     "title": "[3.6] bpo-32720: Fixed the replacement field grammar documentation. (GH-5544)",
                     "body": "\n\n`arg_name` and `element_index` are defined as `digit`+ instead of `integer`.\n(cherry picked from commit 7a561afd2c79f63a6008843b83733911d07f0119)\n\nCo-authored-by: Mariatta <Mariatta@users.noreply.github.com>",
-                    "labels": [{"name": "CLA signed",}, {"name": "awaiting merge",}],
+                    "labels": [
+                        {
+                            "name": "CLA signed",
+                        },
+                        {
+                            "name": "awaiting merge",
+                        },
+                    ],
                     "issue_url": "/repos/python/cpython/issues/5547",
                 }
             ],
@@ -761,7 +838,14 @@ async def test_new_commit_pushed_to_not_approved_pr():
                     "number": 5547,
                     "title": "[3.6] bpo-32720: Fixed the replacement field grammar documentation. (GH-5544)",
                     "body": "\n\n`arg_name` and `element_index` are defined as `digit`+ instead of `integer`.\n(cherry picked from commit 7a561afd2c79f63a6008843b83733911d07f0119)\n\nCo-authored-by: Mariatta <Mariatta@users.noreply.github.com>",
-                    "labels": [{"name": "CLA signed",}, {"name": "awaiting review",}],
+                    "labels": [
+                        {
+                            "name": "CLA signed",
+                        },
+                        {
+                            "name": "awaiting review",
+                        },
+                    ],
                     "issue_url": "/repos/python/cpython/issues/5547",
                 }
             ],
diff --git a/tests/test_util.py b/tests/test_util.py
index bbd34803..7f275b91 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -2,6 +2,7 @@
 
 import gidgethub
 import pytest
+from unittest.mock import patch
 
 from bedevere import util
 
@@ -157,3 +158,36 @@ async def test_get_pr_for_commit_not_found():
     result = await util.get_pr_for_commit(gh, sha)
 
     assert result is None
+
+
+async def test_patch_body_adds_issue_if_not_present():
+    """Updates the description of a PR with the gh issue number if it exists.
+
+    returns if body exists with issue_number
+    """
+    sha = "f2393593c99dd2d3ab8bfab6fcc5ddee540518a9"
+    gh = FakeGH(
+        getitem={
+            f"https://api.github.com/search/issues?q=type:pr+repo:python/cpython+sha:{sha}": {
+                "total_count": 0,
+                "items": [],
+            }
+        }
+    )
+    vals = {}
+    vals["url"] = "https://fake.com"
+    vals["body"] = "GH-1234\n"
+
+    with patch.object(gh, "patch") as mock:
+        await util.patch_body(gh, vals, "1234")
+        mock.assert_not_called()
+    with patch.object(gh, "patch") as mock:
+        vals["body"] = None
+        await util.patch_body(gh, vals, "1234")
+        mock.assert_called_once()
+    with patch.object(gh, "patch") as mock:
+        vals["body"] = ""
+        await util.patch_body(gh, vals, "1234")
+        data = "\n\n<!-- gh-issue-number: gh-1234 -->\n* gh-1234\n<!-- /gh-issue-number -->\n"
+        mock.assert_called_once_with("https://fake.com", data=data)
+    assert await gh.patch(vals["url"], data=vals) == None