diff --git a/requirements/dev.in b/requirements/dev.in
index 63f4c778c7..491b119439 100644
--- a/requirements/dev.in
+++ b/requirements/dev.in
@@ -68,3 +68,6 @@ importlib-resources
 
 # Needed for using integration logo svg files as bot avatars
 cairosvg
+
+# Needed for tools/check-thirdparty
+python-debian
diff --git a/requirements/dev.txt b/requirements/dev.txt
index 2412aa024e..d547e6a43a 100644
--- a/requirements/dev.txt
+++ b/requirements/dev.txt
@@ -164,7 +164,7 @@ cfn-lint==0.29.5 \
 chardet==3.0.4 \
     --hash=sha256:84ab92ed1c4d4f16916e05906b6b75a6c0fb5db821cc65e70cbd64a3e2a5eaae \
     --hash=sha256:fc323ffcaeaed0e0a02bf4d117757b98aed530d9ed4531e3e15460124c106691 \
-    # via requests, talon
+    # via python-debian, requests, talon
 click==7.0 \
     --hash=sha256:2335065e6395b9e67ca716de5f7526736bfa6ceead690adf616d925bdc622b13 \
     --hash=sha256:5b94b49521f6456670fdb30cd82a4eca9412788a93fa6dd6df72c94d5a8ff2d7 \
@@ -725,6 +725,10 @@ python-dateutil==2.8.1 \
     --hash=sha256:73ebfe9dbf22e832286dafa60473e4cd239f8592f699aa5adaf10050e6e1823c \
     --hash=sha256:75bb3f31ea686f1197762692a9ee6a7550b59fc6ca3a1f4b5d7e32fb98e2da2a \
     # via -r requirements/common.in, arrow, botocore, hypchat, moto
+python-debian==0.1.37 \
+    --hash=sha256:847890c158ae77f3d09bc6da10ae6cb4f2c2a5fb6d874528c6e076417d5fd333 \
+    --hash=sha256:ab04f535155810c46c8abf3f7d46364b67b034c49ff8690cdb510092eee56750 \
+    # via -r requirements/dev.in
 python-digitalocean==1.15.0 \
     --hash=sha256:e318fe7b866ae00820f7ecec690a9320337f88c6e645310bf92f9b491148122a \
     # via -r requirements/dev.in
@@ -846,7 +850,7 @@ sh==1.12.14 \
 six==1.14.0 \
     --hash=sha256:236bdbdce46e6e6a3d61a337c0f8b763ca1e8717c03b369e87a7ec7ce1319c0a \
     --hash=sha256:8f3cd2e254d8f793e7f3d6d9df77b92252b52637291d0f0da013c76ea2724b6c \
-    # via -r requirements/common.in, argon2-cffi, automat, aws-sam-translator, cfn-lint, cryptography, django-bitfield, docker, ecdsa, hypchat, isodate, jsonschema, libthumbor, mock, moto, packaging, parsel, pip-tools, prompt-toolkit, protego, pyopenssl, python-dateutil, python-jose, qrcode, responses, social-auth-app-django, social-auth-core, talon, traitlets, twilio, w3lib, websocket-client, zulint, zulip
+    # via -r requirements/common.in, argon2-cffi, automat, aws-sam-translator, cfn-lint, cryptography, django-bitfield, docker, ecdsa, hypchat, isodate, jsonschema, libthumbor, mock, moto, packaging, parsel, pip-tools, prompt-toolkit, protego, pyopenssl, python-dateutil, python-debian, python-jose, qrcode, responses, social-auth-app-django, social-auth-core, talon, traitlets, twilio, w3lib, websocket-client, zulint, zulip
 snakeviz==2.0.1 \
     --hash=sha256:5e30f144edb17d875b46cb5f82bd3e67fb5018e534ecc1a94e092ef3ce932c25 \
     --hash=sha256:80acc9c204aeb1e089f209a4c79bb5940dc40b6536a5184c1778a3f448634885 \
diff --git a/tools/check-thirdparty b/tools/check-thirdparty
new file mode 100755
index 0000000000..501b8f5c98
--- /dev/null
+++ b/tools/check-thirdparty
@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+"""Check the docs/THIRDPARTY file against the DEP-5 copyright format.
+
+https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+
+Disclaimer: This script is not a lawyer.  It cannot validate that the
+claimed licenses are correct.  It can only check for basic syntactic
+issues.
+"""
+
+import difflib
+import io
+import os
+import subprocess
+import sys
+from debian import copyright
+
+COPYRIGHT_FILENAME = "docs/THIRDPARTY"
+os.chdir(os.path.join(os.path.dirname(__file__), ".."))
+status = 0
+
+*files, empty = subprocess.check_output(
+    ["git", "ls-files", "-z"], encoding="utf-8",
+).split("\0")
+assert empty == ""
+files += [
+    "static/generated/emoji/images/emoji/unicode/ignore-this-path",
+]
+
+with open(COPYRIGHT_FILENAME) as f:
+    lines = list(f)
+c = copyright.Copyright(lines)
+
+if not c.header.known_format():
+    print(f"{COPYRIGHT_FILENAME}: Unknown header format {c.header.format}")
+    status = 1
+
+defined_licenses = {
+    p.license.synopsis for p in c.all_license_paragraphs() if p.license.text
+}
+
+for p in c.all_files_paragraphs():
+    for g in p.files:
+        if not any(map(copyright.globs_to_re([g]).fullmatch, files)):
+            print(f"{COPYRIGHT_FILENAME}: No such file {g}")
+            status = 1
+
+    if not p.license.text and p.license.synopsis not in defined_licenses:
+        print(f"{COPYRIGHT_FILENAME}: Missing license text for {p.license.synopsis}")
+        status = 1
+
+dumped = c.dump()
+if dumped != "".join(lines):
+    print(f"{COPYRIGHT_FILENAME}: Changes expected:")
+    sys.stdout.writelines(
+        difflib.unified_diff(
+            lines,
+            io.StringIO(dumped).readlines(),
+            COPYRIGHT_FILENAME,
+            COPYRIGHT_FILENAME,
+        ),
+    )
+    status = 1
+
+sys.exit(status)
diff --git a/tools/lint b/tools/lint
index 9d0d069d47..14429c1331 100755
--- a/tools/lint
+++ b/tools/lint
@@ -94,6 +94,9 @@ def run() -> None:
                                   description="Syntactic Grep (semgrep) Code Search Tool "
                                   "(config: ./tools/semgrep.yml)")
 
+    linter_config.external_linter('thirdparty', ['tools/check-thirdparty'],
+                                  description="Check docs/THIRDPARTY copyright file syntax")
+
     @linter_config.lint
     def custom_py() -> int:
         """Runs custom checks for python files (config: tools/linter_lib/custom_check.py)"""
diff --git a/version.py b/version.py
index dbd38e2310..10043eeb0d 100644
--- a/version.py
+++ b/version.py
@@ -44,4 +44,4 @@ API_FEATURE_LEVEL = 2
 #   historical commits sharing the same major version, in which case a
 #   minor version bump suffices.
 
-PROVISION_VERSION = '81.3'
+PROVISION_VERSION = '81.4'