diff --git a/tools/mypy.ini b/tools/mypy.ini
index a80ecfd30c880a..e32acd468ff057 100644
--- a/tools/mypy.ini
+++ b/tools/mypy.ini
@@ -33,6 +33,9 @@ ignore_missing_imports = True
 [mypy-html5lib.*]
 ignore_missing_imports = True
 
+[mypy-mod_pywebsocket.*]
+ignore_missing_imports = True
+
 [mypy-mozdevice.*]
 ignore_missing_imports = True
 
@@ -90,7 +93,7 @@ disallow_untyped_defs = False
 disallow_untyped_defs = False
 
 [mypy-tools.serve.*]
-ignore_errors = True
+disallow_untyped_defs = False
 
 [mypy-tools.wave.*]
 disallow_untyped_defs = False
diff --git a/tools/serve/serve.py b/tools/serve/serve.py
index 1d70952a8e4e88..2fde7114f6802a 100644
--- a/tools/serve/serve.py
+++ b/tools/serve/serve.py
@@ -1,7 +1,3 @@
-# -*- coding: utf-8 -*-
-
-from __future__ import print_function
-
 import abc
 import argparse
 import importlib
@@ -21,10 +17,11 @@
 import uuid
 from collections import defaultdict, OrderedDict
 from itertools import chain, product
+from typing import ClassVar, List, Set, Tuple
 
-from localpaths import repo_root
+from localpaths import repo_root  # type: ignore
 
-from manifest.sourcefile import read_script_metadata, js_meta_re, parse_variants
+from manifest.sourcefile import read_script_metadata, js_meta_re, parse_variants  # type: ignore
 from wptserve import server as wptserve, handlers
 from wptserve import stash
 from wptserve import config
@@ -62,7 +59,7 @@ class WrapperHandler(object):
 
     __meta__ = abc.ABCMeta
 
-    headers = []
+    headers = []  # type: ClassVar[List[Tuple[str, str]]]
 
     def __init__(self, base_path=None, url_base="/"):
         self.base_path = base_path
@@ -180,7 +177,7 @@ def check_exposure(self, request):
 
 
 class HtmlWrapperHandler(WrapperHandler):
-    global_type = None
+    global_type = None  # type: ClassVar[str]
     headers = [('Content-Type', 'text/html')]
 
     def check_exposure(self, request):
@@ -892,10 +889,10 @@ def iter_procs(servers):
             yield server.proc
 
 
-def _make_subdomains_product(s, depth=2):
+def _make_subdomains_product(s: Set[str], depth: int = 2) -> Set[str]:
     return {u".".join(x) for x in chain(*(product(s, repeat=i) for i in range(1, depth+1)))}
 
-def _make_origin_policy_subdomains(limit):
+def _make_origin_policy_subdomains(limit: int) -> Set[str]:
     return {u"op%d" % x for x in range(1,limit+1)}
 
 
diff --git a/tools/serve/test_functional.py b/tools/serve/test_functional.py
index c30ca15a145ede..14ea649be86cac 100644
--- a/tools/serve/test_functional.py
+++ b/tools/serve/test_functional.py
@@ -25,7 +25,7 @@ def start(self, *args, **kwargs):
 
         return result
 
-serve.ServerProc = ServerProcSpy
+serve.ServerProc = ServerProcSpy  # type: ignore
 
 @pytest.fixture()
 def server_subprocesses():
diff --git a/tools/serve/test_serve.py b/tools/serve/test_serve.py
index 0a07db7d099292..5a51376c4892c5 100644
--- a/tools/serve/test_serve.py
+++ b/tools/serve/test_serve.py
@@ -4,7 +4,7 @@
 
 import pytest
 
-import localpaths
+import localpaths  # type: ignore
 from . import serve
 from .serve import ConfigBuilder
 
diff --git a/tools/serve/wave.py b/tools/serve/wave.py
index b13c6ef34de2ab..b9eb8df70abd40 100644
--- a/tools/serve/wave.py
+++ b/tools/serve/wave.py
@@ -1,4 +1,7 @@
-# -*- coding: utf-8 -*-
+# The ./wpt serve-wave command is broken, so mypy errors are ignored instead of
+# making untestable changes to the problematic imports.
+# See https://github.com/web-platform-tests/wpt/issues/29024.
+# mypy: ignore-errors
 
 import subprocess
 from manifest import manifest