diff --git a/changelog.d/8330.misc b/changelog.d/8330.misc
index c51370f215..fbfdd52473 100644
--- a/changelog.d/8330.misc
+++ b/changelog.d/8330.misc
@@ -1 +1 @@
-Move lint-related dependencies to package-extra field, update CONTRIBUTING.md to utilise this.
\ No newline at end of file
+Move lint-related dependencies to package-extra field, update CONTRIBUTING.md to utilise this.
diff --git a/changelog.d/8377.misc b/changelog.d/8377.misc
new file mode 100644
index 0000000000..fbfdd52473
--- /dev/null
+++ b/changelog.d/8377.misc
@@ -0,0 +1 @@
+Move lint-related dependencies to package-extra field, update CONTRIBUTING.md to utilise this.
diff --git a/setup.py b/setup.py
index 54ddec8f9f..926b1bc86f 100755
--- a/setup.py
+++ b/setup.py
@@ -94,6 +94,22 @@ ALL_OPTIONAL_REQUIREMENTS = dependencies["ALL_OPTIONAL_REQUIREMENTS"]
 # Make `pip install matrix-synapse[all]` install all the optional dependencies.
 CONDITIONAL_REQUIREMENTS["all"] = list(ALL_OPTIONAL_REQUIREMENTS)
 
+# Developer dependencies should not get included in "all".
+#
+# We pin black so that our tests don't start failing on new releases.
+CONDITIONAL_REQUIREMENTS["lint"] = [
+    "isort==5.0.3",
+    "black==19.10b0",
+    "flake8-comprehensions",
+    "flake8",
+]
+
+# Dependencies which are exclusively required by unit test code. This is
+# NOT a list of all modules that are necessary to run the unit tests.
+# Tests assume that all optional dependencies are installed.
+#
+# parameterized_class decorator was introduced in parameterized 0.7.0
+CONDITIONAL_REQUIREMENTS["test"] = ["mock>=2.0", "parameterized>=0.7.0"]
 
 setup(
     name="matrix-synapse",
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 67f019fd22..288631477e 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -37,6 +37,9 @@ logger = logging.getLogger(__name__)
 # installed when that optional dependency requirement is specified. It is passed
 # to setup() as extras_require in setup.py
 #
+# Note that these both represent runtime dependencies (and the versions
+# installed are checked at runtime).
+#
 # [1] https://pip.pypa.io/en/stable/reference/pip_install/#requirement-specifiers.
 
 REQUIREMENTS = [
@@ -92,20 +95,12 @@ CONDITIONAL_REQUIREMENTS = {
     "oidc": ["authlib>=0.14.0"],
     "systemd": ["systemd-python>=231"],
     "url_preview": ["lxml>=3.5.0"],
-    # Dependencies which are exclusively required by unit test code. This is
-    # NOT a list of all modules that are necessary to run the unit tests.
-    # Tests assume that all optional dependencies are installed.
-    #
-    # parameterized_class decorator was introduced in parameterized 0.7.0
-    "test": ["mock>=2.0", "parameterized>=0.7.0"],
     "sentry": ["sentry-sdk>=0.7.2"],
     "opentracing": ["jaeger-client>=4.0.0", "opentracing>=2.2.0"],
     "jwt": ["pyjwt>=1.6.4"],
     # hiredis is not a *strict* dependency, but it makes things much faster.
     # (if it is not installed, we fall back to slow code.)
     "redis": ["txredisapi>=1.4.7", "hiredis"],
-    # We pin black so that our tests don't start failing on new releases.
-    "lint": ["isort==5.0.3", "black==19.10b0", "flake8-comprehensions", "flake8"],
 }
 
 ALL_OPTIONAL_REQUIREMENTS = set()  # type: Set[str]
@@ -113,7 +108,7 @@ ALL_OPTIONAL_REQUIREMENTS = set()  # type: Set[str]
 for name, optional_deps in CONDITIONAL_REQUIREMENTS.items():
     # Exclude systemd as it's a system-based requirement.
     # Exclude lint as it's a dev-based requirement.
-    if name not in ["systemd", "lint"]:
+    if name not in ["systemd"]:
         ALL_OPTIONAL_REQUIREMENTS = set(optional_deps) | ALL_OPTIONAL_REQUIREMENTS
 
 
diff --git a/tox.ini b/tox.ini
index ddcab0198f..4d132eff4c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,13 +2,12 @@
 envlist = packaging, py35, py36, py37, py38, check_codestyle, check_isort
 
 [base]
+extras = test
 deps =
-    mock
     python-subunit
     junitxml
     coverage
     coverage-enable-subprocess
-    parameterized
 
     # cyptography 2.2 requires setuptools >= 18.5
     #
@@ -36,7 +35,7 @@ setenv =
 [testenv]
 deps =
     {[base]deps}
-extras = all
+extras = all, test
 
 whitelist_externals =
     sh
@@ -84,7 +83,6 @@ deps =
     # Old automat version for Twisted
     Automat == 0.3.0
 
-    mock
     lxml
     coverage
     coverage-enable-subprocess
@@ -97,7 +95,7 @@ commands =
     /bin/sh -c 'python -m synapse.python_dependencies | sed -e "s/>=/==/g" -e "s/psycopg2==2.6//" -e "s/pyopenssl==16.0.0/pyopenssl==17.0.0/" | xargs -d"\n" pip install'
 
     # Install Synapse itself. This won't update any libraries.
-    pip install -e .
+    pip install -e ".[test]"
 
     {envbindir}/coverage run "{envbindir}/trial"  {env:TRIAL_FLAGS:} {posargs:tests} {env:TOXSUFFIX:}