diff --git a/src/ewoks/_requirements/poetry.py b/src/ewoks/_requirements/poetry.py
index e5dfa35..2f3cceb 100644
--- a/src/ewoks/_requirements/poetry.py
+++ b/src/ewoks/_requirements/poetry.py
@@ -222,7 +222,7 @@ def _version_tuple(version: str) -> Tuple[int, ...]:
     return tuple(int(part) for part in version.split(".") if part.isdigit())
 
 
-def _python_env(python: Union[str, Path]) -> Dict[str, str]:
+def _python_env(python: Union[str, Path]) -> Dict[str, Optional[str]]:
     """Poetry searches `PATH` for a python interpreter, which is not necessarily
     a working one. Make sure it finds this interpreter first. The environment of
     a project is the `.venv` directory inside it.
@@ -231,6 +231,10 @@ def _python_env(python: Union[str, Path]) -> Dict[str, str]:
     return {
         "PATH": os.pathsep.join([str(Path(python).parent), path]),
         "POETRY_VIRTUALENVS_IN_PROJECT": "true",
+        # Poetry uses an active virtual or conda environment, for example the one
+        # of `poetry run`, instead of the environment of the project
+        "VIRTUAL_ENV": None,
+        "CONDA_PREFIX": None,
     }
 
 
diff --git a/src/ewoks/_requirements/utils/base_manager.py b/src/ewoks/_requirements/utils/base_manager.py
index 31d15cb..2ae0ef6 100644
--- a/src/ewoks/_requirements/utils/base_manager.py
+++ b/src/ewoks/_requirements/utils/base_manager.py
@@ -326,11 +326,15 @@ def _add_ewoks(
         pass
 
     def _check_output(
-        self, *args: Union[str, Path], extra_env: Optional[Mapping[str, str]] = None
+        self,
+        *args: Union[str, Path],
+        extra_env: Optional[Mapping[str, Optional[str]]] = None,
     ) -> str:
         return process.check_output(*self._cmd_args, *args, extra_env=extra_env)
 
     def _check_call(
-        self, *args: Union[str, Path], extra_env: Optional[Mapping[str, str]] = None
+        self,
+        *args: Union[str, Path],
+        extra_env: Optional[Mapping[str, Optional[str]]] = None,
     ) -> None:
         process.check_call(*self._cmd_args, *args, extra_env=extra_env)
diff --git a/src/ewoks/_requirements/utils/process.py b/src/ewoks/_requirements/utils/process.py
index 8495f2c..1143589 100644
--- a/src/ewoks/_requirements/utils/process.py
+++ b/src/ewoks/_requirements/utils/process.py
@@ -2,6 +2,7 @@
 import os
 import subprocess
 from pathlib import Path
+from typing import Dict
 from typing import Mapping
 from typing import Optional
 from typing import Union
@@ -10,9 +11,11 @@
 
 
 def check_output(
-    *args: Union[str, Path], extra_env: Optional[Mapping[str, str]] = None
+    *args: Union[str, Path], extra_env: Optional[Mapping[str, Optional[str]]] = None
 ) -> str:
-    """
+    """`extra_env` adds environment variables to the current ones, or removes them
+    when their value is `None`.
+
     :raises RuntimeError: command failed
     """
     logger.debug("Capture output of %s", args)
@@ -25,9 +28,11 @@ def check_output(
 
 
 def check_call(
-    *args: Union[str, Path], extra_env: Optional[Mapping[str, str]] = None
+    *args: Union[str, Path], extra_env: Optional[Mapping[str, Optional[str]]] = None
 ) -> None:
-    """
+    """`extra_env` adds environment variables to the current ones, or removes them
+    when their value is `None`.
+
     :raises RuntimeError: command failed
     """
     logger.debug("Execute %s", args)
@@ -39,7 +44,10 @@ def check_call(
         raise RuntimeError(f"Command failed: {args}") from ex
 
 
-def _environment(extra_env: Optional[Mapping[str, str]]) -> Optional[Mapping[str, str]]:
+def _environment(
+    extra_env: Optional[Mapping[str, Optional[str]]],
+) -> Optional[Dict[str, str]]:
     if not extra_env:
         return None
-    return {**os.environ, **extra_env}
+    environment = {**os.environ, **extra_env}
+    return {name: value for name, value in environment.items() if value is not None}
diff --git a/src/ewoks/tests/requirements/test_poetry.py b/src/ewoks/tests/requirements/test_poetry.py
index 1654c9b..26d07f6 100644
--- a/src/ewoks/tests/requirements/test_poetry.py
+++ b/src/ewoks/tests/requirements/test_poetry.py
@@ -1,6 +1,7 @@
 """Tests specific to the poetry package manager."""
 
 import sys
+import venv
 
 import pytest
 
@@ -65,6 +66,24 @@ def test_environments_root(monkeypatch, tmp_path):
     assert PoetryManager().environments_root() == tmp_path
 
 
+@pytest.mark.skipif(PoetryManager().version() is None, reason="poetry is not installed")
+@pytest.mark.parametrize("variable", ["VIRTUAL_ENV", "CONDA_PREFIX"])
+def test_create_environment_with_active_environment(variable, monkeypatch, tmp_path):
+    """The environment is the one of the project, also when another environment is
+    active, for example the one of `poetry run`."""
+    active = tmp_path / "active"
+    venv.create(active)
+    monkeypatch.setenv(variable, str(active))
+    # Poetry ignores the base environment of conda
+    monkeypatch.setenv("CONDA_DEFAULT_ENV", "active")
+
+    environment = PoetryManager().create_environment(
+        tmp_path / "project", PYTHON_VERSION
+    )
+
+    assert environment.exists()
+
+
 def test_environments_root_not_available(caplog):
     """Environments of ewoks when poetry cannot provide its environment directory."""
     manager = PoetryManager("poetry-does-not-exist")