diff --git a/RELEASE-NOTES.md b/RELEASE-NOTES.md
index 172313e36f3..ac313f2877b 100644
--- a/RELEASE-NOTES.md
+++ b/RELEASE-NOTES.md
@@ -5,6 +5,7 @@
 ### Maintenance
 - Mentioned the way to do any random walk with `theano.tensor.cumsum()` in `GaussianRandomWalk` docstrings (see [#4048](https://github.com/pymc-devs/pymc3/pull/4048)).
 - Fixed numerical instability in ExGaussian's logp by preventing `logpow` from returning `-inf` (see [#4050](https://github.com/pymc-devs/pymc3/pull/4050)).
+- Use dill to serialize user defined logp functions in `DensityDist`. The previous serialization code fails if it is used in notebooks on Windows and Mac. `dill` is now a required dependency. (see [#3844](https://github.com/pymc-devs/pymc3/issues/3844)).
 
 ### Documentation
 
diff --git a/environment-dev.yml b/environment-dev.yml
index 5cfa3ec6025..23982a66352 100644
--- a/environment-dev.yml
+++ b/environment-dev.yml
@@ -37,7 +37,7 @@ dependencies:
   - dataclasses  # python_version < 3.7
   - contextvars  # python_version < 3.7
   - mkl-service
+  - dill
   - libblas=*=*mkl
   - pip:
     - black_nbconvert
-    - dill
diff --git a/pymc3/distributions/distribution.py b/pymc3/distributions/distribution.py
index 7176fb47add..2bdf9d88c09 100644
--- a/pymc3/distributions/distribution.py
+++ b/pymc3/distributions/distribution.py
@@ -14,6 +14,7 @@
 
 import numbers
 import contextvars
+import dill
 from typing import TYPE_CHECKING
 if TYPE_CHECKING:
     from typing import Optional, Callable
@@ -419,6 +420,19 @@ def __init__(
         self.wrap_random_with_dist_shape = wrap_random_with_dist_shape
         self.check_shape_in_random = check_shape_in_random
 
+    def __getstate__(self):
+        # We use dill to serialize the logp function, as this is almost
+        # always defined in the notebook and won't be pickled correctly.
+        # Fix https://github.com/pymc-devs/pymc3/issues/3844
+        logp = dill.dumps(self.logp)
+        vals = self.__dict__.copy()
+        vals['logp'] = logp
+        return vals
+
+    def __setstate__(self, vals):
+        vals['logp'] = dill.loads(vals['logp'])
+        self.__dict__ = vals
+
     def random(self, point=None, size=None, **kwargs):
         if self.rand is not None:
             not_broadcast_kwargs = dict(point=point)
diff --git a/pymc3/tests/test_distributions.py b/pymc3/tests/test_distributions.py
index 2897211e9bc..a52ff63a4a3 100644
--- a/pymc3/tests/test_distributions.py
+++ b/pymc3/tests/test_distributions.py
@@ -79,6 +79,7 @@
 
 from ..distributions import continuous
 from pymc3.theanof import floatX
+import pymc3 as pm
 from numpy import array, inf, log, exp
 from numpy.testing import assert_almost_equal, assert_allclose, assert_equal
 import numpy.random as nr
@@ -1872,3 +1873,16 @@ def test_issue_3051(self, dims, dist_cls, kwargs):
         assert isinstance(actual_a, np.ndarray)
         assert actual_a.shape == (X.shape[0],)
         pass
+
+
+def test_serialize_density_dist():
+    def func(x):
+        return -2 * (x ** 2).sum()
+
+    with pm.Model():
+        pm.Normal('x')
+        y = pm.DensityDist('y', func)
+        pm.sample(draws=5, tune=1, mp_ctx="spawn")
+
+    import pickle
+    pickle.loads(pickle.dumps(y))
diff --git a/requirements-dev.txt b/requirements-dev.txt
index f11a4da9b73..13caa0d577d 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -17,4 +17,4 @@ sphinx-autobuild==0.7.1
 sphinx>=1.5.5
 watermark
 parameterized
-dill
\ No newline at end of file
+dill
diff --git a/requirements.txt b/requirements.txt
index c65a007ef10..75aaba286da 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,3 +9,4 @@ h5py>=2.7.0
 typing-extensions>=3.7.4
 dataclasses; python_version < '3.7'
 contextvars; python_version < '3.7' 
+dill
diff --git a/scripts/create_testenv.sh b/scripts/create_testenv.sh
index 6a1e1e516ad..418d3dacc69 100755
--- a/scripts/create_testenv.sh
+++ b/scripts/create_testenv.sh
@@ -22,15 +22,18 @@ command -v conda >/dev/null 2>&1 || {
 ENVNAME="${ENVNAME:-testenv}"         # if no ENVNAME is specified, use testenv
 
 if [ -z ${GLOBAL} ]; then
+  source $(dirname $(dirname $(which conda)))/etc/profile.d/conda.sh
   if conda env list | grep -q ${ENVNAME}; then
     echo "Environment ${ENVNAME} already exists, keeping up to date"
+    conda activate ${ENVNAME}
+    mamba env update -f environment-dev.yml
   else
     conda config --add channels conda-forge
     conda config --set channel_priority strict
     conda install -c conda-forge mamba --yes
     mamba env create -f environment-dev.yml
+    conda activate ${ENVNAME}
   fi
-  source activate ${ENVNAME}
 fi
 
 #  Install editable using the setup.py