diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index 7edb009d..7c7a999b 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -42,9 +42,12 @@ jobs:
         coverage3 run -m unittest discover --start-directory tests --verbose
         coverage3 report
     - name: Type check with Mypy
-      run: |
-        mypy
+      run: mypy
     - name: Lint with Flake8 and isort
       run: |
         flake8 *\.py pottery/*\.py tests/*\.py --count --max-complexity=10 --statistics
         isort *\.py pottery/*\.py tests/*\.py --check-only --diff
+    - name: Check for security vulnerabilities with Bandit and Safety
+      run: |
+        bandit -r pottery
+        safety check
diff --git a/pottery/monkey.py b/pottery/monkey.py
index d5b61417..98dcffb3 100644
--- a/pottery/monkey.py
+++ b/pottery/monkey.py
@@ -19,9 +19,11 @@
 
 import logging
 from typing import Any
+from typing import Callable
 from typing import Dict
 from typing import List
 from typing import Union
+from typing import cast
 
 # TODO: When we drop support for Python 3.7, change the following import to:
 #   from typing import Final
@@ -37,12 +39,19 @@
 # already knows how to JSONify dicts, lists, and strings).
 
 def _default(self: Any, obj: Any) -> Union[Dict[str, Any], List[Any], str]:
-    func_names = {'to_dict', 'to_list', 'to_str'}
-    funcs = {getattr(obj.__class__, name, None) for name in func_names}
-    funcs.discard(None)
-    assert len(funcs) <= 1
-    func = funcs.pop() if any(funcs) else _default.default  # type: ignore
-    return_value = func(obj)  # type: ignore
+    method_names = ('to_dict', 'to_list', 'to_str')
+    methods = tuple(getattr(obj.__class__, name, None) for name in method_names)
+    methods = tuple(method for method in methods if method is not None)
+    if len(methods) > 1:
+        methods_defined = ', '.join(
+            cast(Callable, method).__qualname__ + '()' for method in methods
+        )
+        raise TypeError(
+            f"{methods_defined} defined; "
+            f"don't know how to JSONify {obj.__class__.__name__} objects"
+        )
+    method = methods[0] if methods else _default.default  # type: ignore
+    return_value = method(obj)  # type: ignore
     return return_value
 
 import json  # isort: skip
diff --git a/pottery/queue.py b/pottery/queue.py
index 70d2c115..87b6b0b4 100644
--- a/pottery/queue.py
+++ b/pottery/queue.py
@@ -105,7 +105,7 @@ def get(self,
                 except (WatchError, IndexError):
                     if not block or timer.elapsed() / 1000 >= (timeout or 0):
                         raise QueueEmptyError(redis=self.redis, key=self.key)
-                    delay = random.uniform(0, self.RETRY_DELAY/1000)
+                    delay = random.uniform(0, self.RETRY_DELAY/1000)  # nosec
                     time.sleep(delay)
 
     __get = get
diff --git a/pottery/redlock.py b/pottery/redlock.py
index b0c2262c..6929b652 100644
--- a/pottery/redlock.py
+++ b/pottery/redlock.py
@@ -441,7 +441,7 @@ def log_time_enqueued(timer: ContextTimer, acquired: bool) -> None:
                             log_time_enqueued(timer, True)
                         return True
                     enqueued = True
-                    delay = random.uniform(0, self.RETRY_DELAY/1000)
+                    delay = random.uniform(0, self.RETRY_DELAY/1000)  # nosec
                     time.sleep(delay)
             if enqueued:
                 log_time_enqueued(timer, False)
diff --git a/requirements-to-freeze.txt b/requirements-to-freeze.txt
index 0b5ea187..161c04b0 100644
--- a/requirements-to-freeze.txt
+++ b/requirements-to-freeze.txt
@@ -30,6 +30,9 @@ types-redis
 flake8
 isort
 
+bandit
+safety
+
 twine
 
 
diff --git a/requirements.txt b/requirements.txt
index 19c55821..b40905ba 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,11 +1,16 @@
+bandit==1.7.1
 bleach==4.1.0
 certifi==2021.10.8
 charset-normalizer==2.0.10
+click==8.0.3
 colorama==0.4.4
 coverage==6.2
 Deprecated==1.2.13
 docutils==0.18.1
+dparse==0.5.1
 flake8==4.0.1
+gitdb==4.0.9
+GitPython==3.1.26
 hiredis==2.0.0
 idna==3.3
 importlib-metadata==4.2.0
@@ -16,17 +21,23 @@ mmh3==3.0.0
 mypy==0.931
 mypy-extensions==0.4.3
 packaging==21.3
+pbr==5.8.0
 pkginfo==1.8.2
 pycodestyle==2.8.0
 pyflakes==2.4.0
 Pygments==2.11.2
 pyparsing==3.0.6
+PyYAML==6.0
 readme-renderer==32.0
 redis==4.1.0
 requests==2.27.1
 requests-toolbelt==0.9.1
 rfc3986==2.0.0
+safety==1.10.3
 six==1.16.0
+smmap==5.0.0
+stevedore==3.5.0
+toml==0.10.2
 tomli==2.0.0
 tqdm==4.62.3
 twine==3.7.1
diff --git a/tests/test_monkey.py b/tests/test_monkey.py
index 090af223..7bc51af0 100644
--- a/tests/test_monkey.py
+++ b/tests/test_monkey.py
@@ -21,9 +21,37 @@
 from tests.base import TestCase
 
 
+class Incorrect:
+    def to_dict(self):
+        return {}
+
+    def to_list(self):
+        return []
+
+
+class Correct:
+    def to_dict(self):
+        return {}
+
+
 class MonkeyPatchTests(TestCase):
-    def test_json_encoder(self):
+    def test_typeerror_not_jsonifyable(self):
         try:
             json.dumps(object())
         except TypeError as error:
             assert str(error) == 'Object of type object is not JSON serializable'
+
+    def test_typeerror_multiple_methods(self):
+        try:
+            json.dumps(Incorrect())
+        except TypeError as error:
+            assert str(error) == (
+                "Incorrect.to_dict(), Incorrect.to_list() defined; "
+                "don't know how to JSONify Incorrect objects"
+            )
+
+    def test_dict(self):
+        assert json.dumps({}) == '{}'
+
+    def test_to_dict(self):
+        assert json.dumps(Correct()) == '{}'