diff --git a/.github/workflows/fluent.runtime.yml b/.github/workflows/fluent.runtime.yml
index d9531d95..0eb9647c 100644
--- a/.github/workflows/fluent.runtime.yml
+++ b/.github/workflows/fluent.runtime.yml
@@ -39,7 +39,7 @@ jobs:
         run: |
           python -m pip install wheel
           python -m pip install --upgrade pip
-          python -m pip install fluent.syntax==${{ matrix.fluent-syntax }}
+          python -m pip install fluent.syntax==${{ matrix.fluent-syntax }} six
           python -m pip install .
       - name: Test
         working-directory: ./fluent.runtime
@@ -53,11 +53,16 @@ jobs:
         with:
           python-version: 3.9
       - name: Install dependencies
+        working-directory: ./fluent.runtime
         run: |
           python -m pip install wheel
           python -m pip install --upgrade pip
-          python -m pip install flake8==6
-          python -m pip install mypy==1
+          python -m pip install .
+          python -m pip install flake8==6 mypy==1
+      - name: Install latest fluent.syntax
+        working-directory: ./fluent.syntax
+        run: |
+          python -m pip install .
       - name: flake8
         working-directory: ./fluent.runtime
         run: |
diff --git a/.github/workflows/fluent.syntax.yml b/.github/workflows/fluent.syntax.yml
index 46a9b5ab..6eedbf6e 100644
--- a/.github/workflows/fluent.syntax.yml
+++ b/.github/workflows/fluent.syntax.yml
@@ -35,6 +35,7 @@ jobs:
         run: |
           python -m pip install wheel
           python -m pip install --upgrade pip
+          python -m pip install .
       - name: Test
         working-directory: ./fluent.syntax
         run: |
@@ -47,10 +48,11 @@ jobs:
         with:
           python-version: 3.9
       - name: Install dependencies
+        working-directory: ./fluent.syntax
         run: |
           python -m pip install --upgrade pip
-          python -m pip install flake8==6
-          python -m pip install mypy==1
+          python -m pip install .
+          python -m pip install flake8==6 mypy==1
       - name: flake8
         working-directory: ./fluent.syntax
         run: |
diff --git a/fluent.docs/setup.py b/fluent.docs/setup.py
index 15436d93..138d54d9 100644
--- a/fluent.docs/setup.py
+++ b/fluent.docs/setup.py
@@ -1,6 +1,9 @@
-from setuptools import setup, find_namespace_packages
+from setuptools import setup
 
 setup(
     name='fluent.docs',
-    packages=find_namespace_packages(include=['fluent.*']),
+    packages=['fluent.docs'],
+    install_requires=[
+        'typing-extensions>=3.7,<5'
+    ],
 )
diff --git a/fluent.runtime/fluent/runtime/bundle.py b/fluent.runtime/fluent/runtime/bundle.py
index d068b4b6..ea75cddc 100644
--- a/fluent.runtime/fluent/runtime/bundle.py
+++ b/fluent.runtime/fluent/runtime/bundle.py
@@ -1,7 +1,8 @@
 import babel
 import babel.numbers
 import babel.plural
-from typing import Any, Callable, Dict, List, Literal, TYPE_CHECKING, Tuple, Union, cast
+from typing import Any, Callable, Dict, List, TYPE_CHECKING, Tuple, Union, cast
+from typing_extensions import Literal
 
 from fluent.syntax import ast as FTL
 
diff --git a/fluent.runtime/fluent/runtime/resolver.py b/fluent.runtime/fluent/runtime/resolver.py
index 301bc0f1..e4d0caa5 100644
--- a/fluent.runtime/fluent/runtime/resolver.py
+++ b/fluent.runtime/fluent/runtime/resolver.py
@@ -68,9 +68,7 @@ def modified(self, **replacements: Any) -> Generator['ResolverEnvironment', None
         yield self
         self.current = old_current
 
-    def modified_for_term_reference(
-            self, args: Union[Dict[str, Any], None] = None
-    ) -> contextlib._GeneratorContextManager['ResolverEnvironment']:
+    def modified_for_term_reference(self, args: Union[Dict[str, Any], None] = None) -> Any:
         return self.modified(args=args if args is not None else {},
                              error_for_missing_arg=False)
 
diff --git a/fluent.runtime/fluent/runtime/types.py b/fluent.runtime/fluent/runtime/types.py
index 24e18796..a10b254d 100644
--- a/fluent.runtime/fluent/runtime/types.py
+++ b/fluent.runtime/fluent/runtime/types.py
@@ -7,7 +7,8 @@
 from babel import Locale
 from babel.dates import format_date, format_time, get_datetime_format, get_timezone
 from babel.numbers import NumberPattern, parse_pattern
-from typing import Any, Dict, Literal, Type, TypeVar, Union, cast
+from typing import Any, Dict, Type, TypeVar, Union, cast
+from typing_extensions import Literal
 
 FORMAT_STYLE_DECIMAL = "decimal"
 FORMAT_STYLE_CURRENCY = "currency"
diff --git a/fluent.runtime/setup.py b/fluent.runtime/setup.py
index d9c5e631..41a5e11e 100755
--- a/fluent.runtime/setup.py
+++ b/fluent.runtime/setup.py
@@ -33,6 +33,7 @@
           'attrs',
           'babel',
           'pytz',
+          'typing-extensions>=3.7,<5'
       ],
       test_suite='tests',
       )
diff --git a/fluent.runtime/tox.ini b/fluent.runtime/tox.ini
index c0f3920d..511cb53c 100644
--- a/fluent.runtime/tox.ini
+++ b/fluent.runtime/tox.ini
@@ -12,6 +12,7 @@ deps =
      attrs==19.1.0
      babel==2.7.0
      pytz==2019.2
+     typing-extensions==3.7
      syntax: .
 commands = ./runtests.py
 
diff --git a/fluent.syntax/fluent/syntax/ast.py b/fluent.syntax/fluent/syntax/ast.py
index e22f86b7..d2e48490 100644
--- a/fluent.syntax/fluent/syntax/ast.py
+++ b/fluent.syntax/fluent/syntax/ast.py
@@ -208,10 +208,10 @@ def parse(self) -> Dict[str, Any]:
 
 class StringLiteral(Literal):
     def parse(self) -> Dict[str, str]:
-        def from_escape_sequence(matchobj: re.Match[str]) -> str:
+        def from_escape_sequence(matchobj: Any) -> str:
             c, codepoint4, codepoint6 = matchobj.groups()
             if c:
-                return c
+                return cast(str, c)
             codepoint = int(codepoint4 or codepoint6, 16)
             if codepoint <= 0xD7FF or 0xE000 <= codepoint:
                 return chr(codepoint)
diff --git a/fluent.syntax/fluent/syntax/stream.py b/fluent.syntax/fluent/syntax/stream.py
index 41035a10..150ac933 100644
--- a/fluent.syntax/fluent/syntax/stream.py
+++ b/fluent.syntax/fluent/syntax/stream.py
@@ -1,4 +1,5 @@
-from typing import Callable, Literal, Union
+from typing import Callable, Union
+from typing_extensions import Literal
 from .errors import ParseError
 
 
diff --git a/fluent.syntax/setup.py b/fluent.syntax/setup.py
index 8c1f95eb..23c17064 100644
--- a/fluent.syntax/setup.py
+++ b/fluent.syntax/setup.py
@@ -26,5 +26,8 @@
       ],
       packages=['fluent.syntax'],
       package_data={'fluent.syntax': ['py.typed']},
+      install_requires=[
+          'typing-extensions>=3.7,<5'
+      ],
       test_suite='tests.syntax'
       )
diff --git a/fluent.syntax/tox.ini b/fluent.syntax/tox.ini
index 2ed33bdb..db0448bc 100644
--- a/fluent.syntax/tox.ini
+++ b/fluent.syntax/tox.ini
@@ -7,4 +7,6 @@ skipsdist=True
 [testenv]
 setenv =
     PYTHONPATH = {toxinidir}
+deps =
+     typing-extensions==3.7
 commands = ./runtests.py