diff --git a/.github/workflows/cicd.yml b/.github/workflows/cicd.yml
index b5b7e9e..4393175 100644
--- a/.github/workflows/cicd.yml
+++ b/.github/workflows/cicd.yml
@@ -181,7 +181,7 @@ jobs:
     timeout-minutes: 30
     strategy:
       matrix:
-        python: ["2.7", "3.5", "3.6", "3.7", "3.8", "3.9", "pypy2", "pypy3"]
+        python: ["2.7", "3.5", "3.6", "3.7", "3.8", "3.9"]#, "pypy2.7", "pypy3.9"]
 
     steps:
 
@@ -189,7 +189,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Install Python
-        uses: actions/setup-python@v1
+        uses: MatteoH2O1999/setup-python@v4
         with:
           python-version: ${{ matrix.python }}
 
@@ -204,7 +204,7 @@ jobs:
           set -eux
           py="${{ matrix.python }}";
           if [[ $py =~ pypy ]]; then  # PyPy
-              py_test="${py}";
+              py_test="${py/./}"; # remove "."
           else  # CPython
               py_test="py${py/./}";  # Add "py" prefix, remove "."
           fi;
@@ -215,7 +215,7 @@ jobs:
 
       - name: Upload pytest log artifact
         if: failure()
-        uses: actions/upload-artifact@v1
+        uses: actions/upload-artifact@v4
         with:
           name: pytest-logs
           path: pytest-logs.tgz
diff --git a/src/hyperlink/_url.py b/src/hyperlink/_url.py
index 8797b5c..e37dd83 100644
--- a/src/hyperlink/_url.py
+++ b/src/hyperlink/_url.py
@@ -1188,6 +1188,22 @@ def user(self):
         """
         return self.userinfo.split(u":")[0]
 
+    @property
+    def _host_idna_error(self):
+        # type: () -> bool
+        """Whether idna can encode the host
+
+        idna does not encode empty strings and ipv6 addresses.
+        This is by design.
+        """
+        if not hasattr(self, "_host_is_ipv6_literal"):
+            try:
+                socket.inet_pton(socket.AF_INET6, self.host)
+                self._host_is_ipv6_literal = True
+            except OSError:
+                self._host_is_ipv6_literal = False
+        return self._host_is_ipv6_literal or not self.host
+
     def authority(self, with_password=False, **kw):
         # type: (bool, Any) -> Text
         """Compute and return the appropriate host/port/userinfo combination.
@@ -1669,7 +1685,7 @@ def to_uri(self):
         )
         new_host = (
             self.host
-            if not self.host
+            if self._host_idna_error
             else idna_encode(self.host, uts46=True).decode("ascii")
         )
         return self.replace(
diff --git a/tox.ini b/tox.ini
index 8865d17..712c942 100644
--- a/tox.ini
+++ b/tox.ini
@@ -44,28 +44,28 @@ basepython =
     py39: python3.9
     py310: python3.10
 
-    pypy2: pypy
-    pypy3: pypy3
+    pypy27: pypy
+    pypy39: pypy3
 
 deps =
     {[default]deps}
 
     # In Python 2, we need to pull in typing, mock
-    py{26,27,py2}: typing==3.10.0.0
-    py{26,27,py2}: mock==3.0.5  # rq.filter: <4
+    py{26,27,py27}: typing==3.10.0.0
+    py{26,27,py27}: mock==3.0.5  # rq.filter: <4
 
     # For pytest
-    py{26,27,34,py2}: pytest==4.6.11  # rq.filter: <5
-    py{35,36,37,38,39,py3}: pytest==5.2.4
+    py{26,27,34,py27}: pytest==4.6.11  # rq.filter: <5
+    py{35,36,37,38,39,py39}: pytest==5.2.4
 
     # For code coverage
     {[testenv:coverage_report]deps}
-    py{26,27,34,py2}: pytest-cov==2.8.1  # rq.filter: <2.9
-    py{35,36,37,38,39,py3}: pytest-cov==2.10.1
+    py{26,27,34,py27}: pytest-cov==2.8.1  # rq.filter: <2.9
+    py{35,36,37,38,39,py39}: pytest-cov==2.10.1
 
     # For hypothesis. Note Python 3.4 isn't supported by hypothesis.
-    py{26,27,py2}: hypothesis==4.43.9  # rq.filter: <4.44
-    py{35,36,37,38,39,py3}: hypothesis==5.8.6
+    py{26,27,py27}: hypothesis==4.43.9  # rq.filter: <4.44
+    py{35,36,37,38,39,py39}: hypothesis==5.8.6
 
 setenv =
     {[default]setenv}
@@ -93,7 +93,8 @@ basepython = {[default]basepython}
 skip_install = True
 
 deps =
-    black==21.7b0
+    black==21.12b0
+    click==8.0.4
 
 setenv =
     BLACK_LINT_ARGS=--check
@@ -325,6 +326,12 @@ basepython = {[default]basepython}
 deps =
     Sphinx==4.1.2
     sphinx-rtd-theme==0.5.2
+    sphinxcontrib-applehelp==1.0.4
+    sphinxcontrib-devhelp==1.0.2
+    sphinxcontrib-devhelp==1.0.2
+    sphinxcontrib-htmlhelp==2.0.1
+    sphinxcontrib-qthelp==1.0.3
+    sphinxcontrib-serializinghtml==1.1.5
 
 commands =
     sphinx-build                           \
@@ -367,6 +374,7 @@ deps =
    check-manifest==0.46
    readme-renderer==29.0
    twine==3.4.2
+   bleach==4.1.0
 
 commands =
    check-manifest