diff --git a/scripts/setup/generate_secrets.py b/scripts/setup/generate_secrets.py
index bd04d79da7..29411bdd0a 100755
--- a/scripts/setup/generate_secrets.py
+++ b/scripts/setup/generate_secrets.py
@@ -61,7 +61,7 @@ def get_old_conf(output_filename):
     secrets_file = six.moves.configparser.RawConfigParser()
     secrets_file.read(output_filename)
 
-    return dict(secrets_file.items("secrets"))  # type: ignore
+    return dict(secrets_file.items("secrets"))  # type: ignore # likely typeshed issue
 
 def generate_secrets(development=False):
     # type: (bool) -> None
diff --git a/tools/linter_lib/custom_check.py b/tools/linter_lib/custom_check.py
index 17d893dcf4..d2358bae83 100644
--- a/tools/linter_lib/custom_check.py
+++ b/tools/linter_lib/custom_check.py
@@ -205,6 +205,11 @@ def build_custom_checkers(by_lang):
          'description': 'Use `is None` to check whether something is None'},
         {'pattern': "type:[(]",
          'description': 'Missing whitespace after ":" in type annotation'},
+        {'pattern': "type: ignore$",
+         'exclude': set(['tools/tests',
+                         'zerver/lib/test_runner.py',
+                         'zerver/tests']),
+         'description': '"type: ignore" should always end with "# type: ignore # explanation for why"'},
         {'pattern': "# type [(]",
          'description': 'Missing : after type in type annotation'},
         {'pattern': "#type",
diff --git a/zerver/lib/bot_lib.py b/zerver/lib/bot_lib.py
index 0ea790e0c5..e74010117f 100644
--- a/zerver/lib/bot_lib.py
+++ b/zerver/lib/bot_lib.py
@@ -76,5 +76,5 @@ class EmbeddedBotHandler(object):
             our_dir, '..', 'bots', bot_name, bot_name + '.conf'))
         section = section or bot_name
         config = configparser.ConfigParser()
-        config.readfp(open(conf_file_path))  # type: ignore
+        config.readfp(open(conf_file_path))  # type: ignore # likely typeshed issue
         return dict(config.items(section))
diff --git a/zerver/lib/test_helpers.py b/zerver/lib/test_helpers.py
index e38c87a50a..4fca0b71ab 100644
--- a/zerver/lib/test_helpers.py
+++ b/zerver/lib/test_helpers.py
@@ -171,7 +171,7 @@ def stdout_suppressed():
     """Redirect stdout to /dev/null."""
 
     with open(os.devnull, 'a') as devnull:
-        stdout, sys.stdout = sys.stdout, devnull  # type: ignore
+        stdout, sys.stdout = sys.stdout, devnull  # type: ignore # monkey-patching
         yield stdout
         sys.stdout = stdout
 
diff --git a/zerver/migrations/0077_add_file_name_field_to_realm_emoji.py b/zerver/migrations/0077_add_file_name_field_to_realm_emoji.py
index 09255452a4..c58b0da283 100644
--- a/zerver/migrations/0077_add_file_name_field_to_realm_emoji.py
+++ b/zerver/migrations/0077_add_file_name_field_to_realm_emoji.py
@@ -97,7 +97,7 @@ class LocalUploader(Uploader):
     def write_local_file(self, path, file_data):
         # type: (Text, binary_type) -> None
         self.mkdirs(path)
-        with open(path, 'wb') as f:   # type: ignore
+        with open(path, 'wb') as f:  # type: ignore # likely mypy bug
             f.write(file_data)
 
     def upload_files(self, response, resized_image, dst_path_id):
diff --git a/zproject/backends.py b/zproject/backends.py
index 929f768937..65326e1db2 100644
--- a/zproject/backends.py
+++ b/zproject/backends.py
@@ -244,7 +244,7 @@ class SocialAuthMixin(ZulipAuthMixin):
         """
         try:
             # Call the auth_complete method of BaseOAuth2 is Python Social Auth
-            return super(SocialAuthMixin, self).auth_complete(*args, **kwargs)  # type: ignore
+            return super(SocialAuthMixin, self).auth_complete(*args, **kwargs)  # type: ignore # monkey-patching
         except AuthFailed:
             return None
         except SocialAuthBaseException as e: