diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2ace24ede..a37bf0047 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,7 +26,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install -r requirements.txt -r requirements-jax.txt -r requirements-test.txt
+        pip install -r requirements.txt -r requirements-jax.txt -r requirements-flax.txt -r requirements-test.txt
         pip install .
         pip install pytest pytest-xdist
     - name: Print installed dependencies
diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index fb4d8e8fc..02a64ec33 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -27,7 +27,7 @@ jobs:
       run: |
         sudo apt install -y pandoc
         python -m pip install --upgrade pip
-        pip install -r requirements.txt -r requirements-jax.txt -r docs/requirements.txt
+        pip install -r requirements.txt -r requirements-jax.txt -r requirements-flax.txt -r docs/requirements.txt
         pip install .
     - name: Print installed dependencies
       run: |
diff --git a/.github/workflows/integration.yml b/.github/workflows/integration.yml
index cf2fbb342..209ab4905 100644
--- a/.github/workflows/integration.yml
+++ b/.github/workflows/integration.yml
@@ -26,7 +26,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install -r requirements.txt -r requirements-jax.txt -r requirements-test.txt
+        pip install -r requirements.txt -r requirements-jax.txt -r requirements-flax.txt -r requirements-test.txt
         pip install .
         pip install pytest pytest-xdist
     - name: Print installed dependencies
diff --git a/MANIFEST.in b/MANIFEST.in
index 4cc82c5dd..809c60dc2 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -2,5 +2,6 @@ include README.md
 include LICENSE
 include requirements.txt
 include requirements-jax.txt
+include requirements-flax.txt
 include requirements-test.txt
 include haiku/py.typed
diff --git a/haiku/experimental/__init__.py b/haiku/experimental/__init__.py
index 0e85e0809..de99adc68 100644
--- a/haiku/experimental/__init__.py
+++ b/haiku/experimental/__init__.py
@@ -52,9 +52,13 @@
 from haiku._src.summarise import MethodInvocation
 from haiku._src.summarise import ModuleDetails
 from haiku._src.summarise import tabulate
-from haiku.experimental import flax
 from haiku.experimental import jaxpr_info
 
+try:
+  from haiku.experimental import flax  # pylint: disable=g-import-not-at-top
+except ImportError:
+  flax = None
+
 # TODO(tomhennigan): Remove deprecated alias.
 ParamContext = GetterContext
 
diff --git a/readthedocs.yml b/readthedocs.yml
index 7673a0972..4a18649c4 100644
--- a/readthedocs.yml
+++ b/readthedocs.yml
@@ -17,6 +17,7 @@ python:
   install:
     - requirements: requirements.txt
     - requirements: requirements-jax.txt
+    - requirements: requirements-flax.txt
     - requirements: docs/requirements.txt
 
 # Additional formats of documentation to be built apart from HTML
diff --git a/requirements-flax.txt b/requirements-flax.txt
new file mode 100644
index 000000000..1d9051262
--- /dev/null
+++ b/requirements-flax.txt
@@ -0,0 +1 @@
+flax>=0.7.1
diff --git a/requirements.txt b/requirements.txt
index 62588eb19..ed929b68f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,4 +2,3 @@ absl-py>=0.7.1
 jmp>=0.0.2
 numpy>=1.18.0
 tabulate>=0.8.9
-flax>=0.7.1
diff --git a/setup.py b/setup.py
index 25b39b183..f98cb65e0 100644
--- a/setup.py
+++ b/setup.py
@@ -48,7 +48,10 @@ def _parse_requirements(requirements_txt_path):
     # Contained modules and scripts.
     packages=find_namespace_packages(exclude=['*_test.py', 'examples']),
     install_requires=_parse_requirements('requirements.txt'),
-    extras_require={'jax': _parse_requirements('requirements-jax.txt')},
+    extras_require={
+        'jax': _parse_requirements('requirements-jax.txt'),
+        'flax': _parse_requirements('requirements-flax.txt'),
+    },
     tests_require=_parse_requirements('requirements-test.txt'),
     requires_python='>=3.9',
     include_package_data=True,
diff --git a/test.sh b/test.sh
index 7af30f4f7..ed0cfeb08 100755
--- a/test.sh
+++ b/test.sh
@@ -33,7 +33,11 @@ python --version
 
 # Install dependencies.
 python -m pip install --upgrade pip setuptools
-pip install -r requirements.txt -r requirements-jax.txt -r requirements-test.txt
+pip install \
+  -r requirements.txt \
+  -r requirements-jax.txt \
+  -r requirements-flax.txt \
+  -r requirements-test.txt
 python -c 'import jax; print(jax.__version__)'
 
 # Run setup.py to install Haiku itself.