diff --git a/auto_nag/scripts/closed_comment.py b/auto_nag/scripts/closed_comment.py
new file mode 100644
index 000000000..d9d9df688
--- /dev/null
+++ b/auto_nag/scripts/closed_comment.py
@@ -0,0 +1,132 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from libmozdata.bugzilla import Bugzilla
+
+from auto_nag import utils
+from auto_nag.bzcleaner import BzCleaner
+from auto_nag.people import People
+
+
+class ClosedComment(BzCleaner):
+    def __init__(self):
+        super().__init__()
+        self.people = People.get_instance()
+
+    def description(self):
+        return "Closed bugs with a new external comment"
+
+    def handle_bug(self, bug, data):
+        last_comment = bug["comments"][-1]
+        # Ignore a comment if:
+        #   - has any tag (e.g., spam)
+        #   - was posted before closing the bug
+        #   - was posted by:
+        #       - the bug creator
+        #       - the bug assignee
+        #       - an internal user (e.g., a bot or employee)
+        #       - a participant who previously commented on the bug
+        if (
+            last_comment["tags"]
+            or last_comment["creation_time"] <= bug["cf_last_resolved"]
+            or last_comment["creator"] in (bug["creator"], bug["assigned_to"])
+            or self._internal_user(last_comment["creator"])
+            or any(
+                last_comment["creator"] == comment["creator"]
+                and comment["creation_time"] <= bug["cf_last_resolved"]
+                for comment in bug["comments"]
+            )
+        ):
+            return None
+
+        bugid = str(bug["id"])
+        data[bugid] = {
+            "dupe_of": bug["dupe_of"],
+            "is_incomplete": bug["resolution"] == "INCOMPLETE",
+        }
+
+        return bug
+
+    def _internal_user(self, email):
+        return (
+            email.endswith("@mozilla.com")
+            or email.endswith("@softvision.com")
+            or utils.is_bot_email(email)
+            or self.people.is_mozilla(email)
+        )
+
+    def get_bugs(self, date="today", bug_ids=..., chunk_size=None):
+        bugs = super().get_bugs(date, bug_ids, chunk_size)
+
+        dup_bug_ids = {bug["dupe_of"] for bug in bugs.values() if bug["dupe_of"]}
+        dup_bug_is_open = {}
+        if dup_bug_ids:
+            Bugzilla(
+                dup_bug_ids,
+                include_fields=["id", "is_open"],
+                bughandler=self._handle_dup_bug,
+                bugdata=dup_bug_is_open,
+            ).wait()
+
+        for bug_id, bug in list(bugs.items()):
+            if dup_bug_is_open.get(bug["dupe_of"]):
+                dupe_of_id = bug["dupe_of"]
+                self.autofix_changes[bug_id] = {
+                    "comment": {
+                        "body": f"This bug is a duplicate of bug {dupe_of_id}. If you have an input, please comment in bug {dupe_of_id} instead."
+                    },
+                }
+            elif not bug["is_incomplete"]:
+                self.autofix_changes[bug_id] = {
+                    "comment": {
+                        "body": {"body": "This bug is closed. Please file a new bug."}
+                    },
+                }
+
+        return bugs
+
+    def _handle_dup_bug(self, bug, data):
+        data[bug["id"]] = bug["is_open"]
+
+    def ignore_meta(self):
+        return True
+
+    def has_access_to_sec_bugs(self):
+        return False
+
+    def get_bz_params(self, date):
+        fields = [
+            "resolution",
+            "dupe_of",
+            "assigned_to",
+            "creator",
+            "cf_last_resolved",
+            "comments.creator",
+            "comments.creation_time",
+            "comments.tags",
+        ]
+
+        params = {
+            "include_fields": fields,
+            "bug_type": "defect",
+            "bug_status": "__closed__",
+            "resolution_type": "notequals",
+            "resolution": "WONTFIX",
+            "f1": "cf_last_resolved",
+            "o1": "lessthan",
+            "v1": "-5d",
+            "n2": 1,
+            "f2": "longdesc",
+            "o2": "casesubstring",
+            "v2": "Please file a new bug",
+            "f3": "longdesc",
+            "o3": "changedafter",
+            "v3": "-1d",
+        }
+
+        return params
+
+
+if __name__ == "__main__":
+    ClosedComment().run()
diff --git a/runauto_nag_hourly.sh b/runauto_nag_hourly.sh
index 4ffdf64ee..ec78f22a7 100755
--- a/runauto_nag_hourly.sh
+++ b/runauto_nag_hourly.sh
@@ -67,6 +67,9 @@ python -m auto_nag.scripts.closed_dupeme --production
 # Detect spam bugs using bugbug
 python -m auto_nag.scripts.spambug --production
 
+# Suggest opening a new bug when commenting on a closed bug
+python -m auto_nag.scripts.closed_comment --production
+
 # Suggest components for untriaged bugs (hourly, list only bugs on which we acted)
 python -m auto_nag.scripts.component --frequency hourly --production
 
diff --git a/templates/closed_comment.html b/templates/closed_comment.html
new file mode 100644
index 000000000..35b8bd303
--- /dev/null
+++ b/templates/closed_comment.html
@@ -0,0 +1,21 @@
+<p>The following {{ plural('bug has', data, pword='bugs have') }} an external comment after being closed:
+  <table {{ table_attrs }}>
+    <thead>
+      <tr>
+        <th>Bug</th><th>Summary</th>
+      </tr>
+    </thead>
+    <tbody>
+      {% for i, (bugid, summary) in enumerate(data) -%}
+      <tr {% if i % 2 == 0 %}bgcolor="#E0E0E0"{% endif -%}>
+        <td>
+          <a href="https://bugzilla.mozilla.org/show_bug.cgi?id={{ bugid }}">{{ bugid }}</a>
+        </td>
+        <td>
+          {{ summary | e }}
+        </td>
+      </tr>
+      {% endfor -%}
+    </tbody>
+  </table>
+</p>