diff --git a/.github/workflows/create-wheels.yaml b/.github/workflows/create-wheels.yaml
index 86f48414c..7c652c6f3 100644
--- a/.github/workflows/create-wheels.yaml
+++ b/.github/workflows/create-wheels.yaml
@@ -65,7 +65,11 @@ jobs:
           FALCON_ASGI_WRAP_NON_COROUTINES: Y
           FALCON_TESTING_SESSION: Y
         run: |
-          pip install 'tox>=3.20'
+          # TODO(kgriffs): Revisit second half of 2021 to see if we still need to pin tox
+          #
+          #   See also: https://github.com/tox-dev/tox/issues/1777
+          #
+          pip install 'tox==3.20'
           tox -e wheel_check -- ${{ matrix.pytest-extra }}
 
       - name: Get wheel name
@@ -177,7 +181,7 @@ jobs:
           FALCON_ASGI_WRAP_NON_COROUTINES: Y
           FALCON_TESTING_SESSION: Y
         run: |
-          pip install 'tox>=3.20'
+          pip install 'tox==3.20'
           tox -e wheel_check -- ${{ matrix.pytest-extra }}
 
       - name: Get wheel names
@@ -353,7 +357,7 @@ jobs:
           args: |
             bash -c "
             export PATH=/opt/python/${{ matrix.python-version }}/bin:$PATH &&
-            pip install 'tox>=3.20' 'pip>=20' &&
+            pip install 'tox==3.20' 'pip>=20' &&
             tox -e wheel_check -- ${{ matrix.pytest-extra }}
             "
 
@@ -377,7 +381,7 @@ jobs:
           args: |
             bash -c "
             export PATH=/opt/python/${{ matrix.python-version }}/bin:$PATH &&
-            pip install 'tox>=3.20' 'pip>=20' &&
+            pip install 'tox==3.20' 'pip>=20' &&
             tox -e wheel_check -- ${{ matrix.pytest-extra }}
             "
 
diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index 9d8a37412..038b7add9 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -106,10 +106,14 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y libunwind-dev
 
+      # TODO(kgriffs): Revisit second half of 2021 to see if we still need to pin tox
+      #
+      #   See also: https://github.com/tox-dev/tox/issues/1777
+      #
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install coverage tox
+          pip install coverage tox==3.20
           python --version
           pip --version
           tox --version
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 6ca49e6ea..17efd913e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -33,11 +33,11 @@ You can check all this by running the following from within the Falcon project d
 $ tools/mintest.sh
 ```
 
-You may also use Python 3.6 or 3.7 if you don't have 3.8 installed on your system. Substitute "py36" or "py37" as appropriate. For example:
+You may also use Python 3.6 or 3.7 if you don't have 3.8 installed on your system. Substitute "py36" or "py37" as appropriate. Note also that due to a bug introduced in tox version 3.21, you will need to pin to 3.20 in order to run Falcon's test suite. For example:
 
 
 ```bash
-$ pip install -U tox coverage
+$ pip install -U tox==3.20 coverage
 $ rm -f .coverage.*
 $ tox -e pep8 && tox -e py35,py37 && tools/testing/combine_coverage.sh
 ```
@@ -141,11 +141,11 @@ $ xdg-open docs/_build/html/index.html
  following guidelines for docstrings:
    * Docstrings should utilize the [napolean style][docstrings] in order to make them read well, regardless of whether they are viewed through `help()` or on [Read the Docs][rtd].
    * Docstrings should begin with a short (~70 characters or less) summary line that ends in a period.
-       * The summary line should begin immediately after the opening quotes (do not add 
+       * The summary line should begin immediately after the opening quotes (do not add
     a line break before the summary line)
-       * The summary line should describe what it is if it is a class (e.g., "An 
+       * The summary line should describe what it is if it is a class (e.g., "An
     asynchronous, file-like object for reading ASGI streams.")
-       * The summary line should describe what it does when called, if it is a 
+       * The summary line should describe what it does when called, if it is a
      function, structured as an imperative (e.g., "Delete a header that was previously set for this response.")
    * Please try to be consistent with the way existing docstrings are formatted. In particular, note the use of single vs. double backticks as follows:
     * Double backticks
diff --git a/tools/mintest.sh b/tools/mintest.sh
index d3912fda0..b463ff07a 100755
--- a/tools/mintest.sh
+++ b/tools/mintest.sh
@@ -1,6 +1,10 @@
 #!/usr/bin/env bash
 
-pip install -U tox coverage
+# TODO(kgriffs): Revisit second half of 2021 to see if we still need to pin tox
+#
+#   See also: https://github.com/tox-dev/tox/issues/1777
+#
+pip install -U tox==3.20 coverage
 
 rm -f .coverage.*
 
diff --git a/tox.ini b/tox.ini
index 7b60b1fa8..3933f49d5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,7 +9,7 @@
 #
 # Which is equivalent to:
 #
-#   $ pip install -U tox coverage
+#   $ pip install -U tox==3.20 coverage
 #   $ rm -f .coverage.*
 #   $ tox -e pep8 && tox -e py38 && tools/testing/combine_coverage.sh
 #