diff --git a/doc/conf.py b/doc/conf.py
index 81f2392..aa500cb 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -27,6 +27,9 @@
 
 from fluiddyn.util import modification_date
 
+os.environ["FLUIDFFT_BUILD_DOC"] = "1"
+
+
 import fluidfft
 import fluidfft.bench_analysis
 from fluidfft.bench_analysis import plot_scaling
diff --git a/pyproject.toml b/pyproject.toml
index 58c3aea..5a7d167 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,7 +5,7 @@ build-backend = 'mesonpy'
 
 [project]
 name = "fluidfft"
-version = "0.4.0rc1"
+version = "0.4.0rc2"
 description = "Efficient and easy Fast Fourier Transform (FFT) for Python."
 authors = [
     {name = "Pierre Augier", email = "pierre.augier@legi.cnrs.fr"},
diff --git a/src/fluidfft/fft2d/__init__.py b/src/fluidfft/fft2d/__init__.py
index ceac080..91afde8 100644
--- a/src/fluidfft/fft2d/__init__.py
+++ b/src/fluidfft/fft2d/__init__.py
@@ -24,6 +24,7 @@ class :class:`fluidfft.fft2d.operators.OperatorsPseudoSpectral2D` defined in
 
 """
 
+import os
 import sys
 
 from .. import _get_classes
@@ -34,7 +35,7 @@ class :class:`fluidfft.fft2d.operators.OperatorsPseudoSpectral2D` defined in
     "get_classes_mpi",
 ]
 
-if "sphinx" in sys.modules:
+if "FLUIDFFT_BUILD_DOC" in os.environ:
     from .fake_mod_fft2d_for_doc import FFT2dFakeForDoc
 
 
diff --git a/src/fluidfft/fft3d/__init__.py b/src/fluidfft/fft3d/__init__.py
index cafade1..2a574a1 100644
--- a/src/fluidfft/fft3d/__init__.py
+++ b/src/fluidfft/fft3d/__init__.py
@@ -24,6 +24,7 @@ class :class:`fluidfft.fft3d.operators.OperatorsPseudoSpectral3D` defined in
 
 """
 
+import os
 import sys
 
 from .. import _get_classes
@@ -34,7 +35,7 @@ class :class:`fluidfft.fft3d.operators.OperatorsPseudoSpectral3D` defined in
     "get_classes_mpi",
 ]
 
-if "sphinx" in sys.modules:
+if "FLUIDFFT_BUILD_DOC" in os.environ:
     from .fake_mod_fft3d_for_doc import FFT3dFakeForDoc