diff --git a/cyaron/io.py b/cyaron/io.py
index 49c1a08..6bb4cf4 100644
--- a/cyaron/io.py
+++ b/cyaron/io.py
@@ -9,6 +9,7 @@
 import re
 import subprocess
 import tempfile
+import psutil
 from typing import Union, overload, Optional, List
 from io import IOBase
 from . import log
@@ -227,6 +228,22 @@ def __clear(self, file: IOBase, pos: int = 0):
         self.is_first_char[file] = True
         file.seek(pos)
 
+    @staticmethod
+    def _kill_process_and_children(pid: int):
+        try:
+            parent = psutil.Process(pid)
+            while True:
+                children = parent.children()
+                if not children:
+                    break
+                for child in children:
+                    IO._kill_process_and_children(child.pid)
+            parent.kill()
+        except psutil.NoSuchProcess:
+            pass
+        except psutil.AccessDenied:
+            pass
+
     def input_write(self, *args, **kwargs):
         """
         Write every element in *args into the input file. Splits with `separator`.
@@ -293,7 +310,8 @@ def output_gen(
         try:
             output, _ = proc.communicate(timeout=time_limit)
         except subprocess.TimeoutExpired:
-            proc.kill()
+            # proc.kill() # didn't work because `shell=True`.
+            self._kill_process_and_children(proc.pid)
             raise
         else:
             if replace_EOL:
diff --git a/poetry.lock b/poetry.lock
index b1294ef..7b703db 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1,4 +1,4 @@
-# This file is automatically @generated by Poetry 1.8.3 and should not be changed by hand.
+# This file is automatically @generated by Poetry 1.8.4 and should not be changed by hand.
 
 [[package]]
 name = "colorama"
@@ -25,6 +25,36 @@ files = [
 [package.dependencies]
 colorama = {version = "*", markers = "platform_system == \"Windows\""}
 
+[[package]]
+name = "psutil"
+version = "6.1.0"
+description = "Cross-platform lib for process and system monitoring in Python."
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,>=2.7"
+files = [
+    {file = "psutil-6.1.0-cp27-cp27m-macosx_10_9_x86_64.whl", hash = "sha256:ff34df86226c0227c52f38b919213157588a678d049688eded74c76c8ba4a5d0"},
+    {file = "psutil-6.1.0-cp27-cp27m-manylinux2010_i686.whl", hash = "sha256:c0e0c00aa18ca2d3b2b991643b799a15fc8f0563d2ebb6040f64ce8dc027b942"},
+    {file = "psutil-6.1.0-cp27-cp27m-manylinux2010_x86_64.whl", hash = "sha256:000d1d1ebd634b4efb383f4034437384e44a6d455260aaee2eca1e9c1b55f047"},
+    {file = "psutil-6.1.0-cp27-cp27mu-manylinux2010_i686.whl", hash = "sha256:5cd2bcdc75b452ba2e10f0e8ecc0b57b827dd5d7aaffbc6821b2a9a242823a76"},
+    {file = "psutil-6.1.0-cp27-cp27mu-manylinux2010_x86_64.whl", hash = "sha256:045f00a43c737f960d273a83973b2511430d61f283a44c96bf13a6e829ba8fdc"},
+    {file = "psutil-6.1.0-cp27-none-win32.whl", hash = "sha256:9118f27452b70bb1d9ab3198c1f626c2499384935aaf55388211ad982611407e"},
+    {file = "psutil-6.1.0-cp27-none-win_amd64.whl", hash = "sha256:a8506f6119cff7015678e2bce904a4da21025cc70ad283a53b099e7620061d85"},
+    {file = "psutil-6.1.0-cp36-abi3-macosx_10_9_x86_64.whl", hash = "sha256:6e2dcd475ce8b80522e51d923d10c7871e45f20918e027ab682f94f1c6351688"},
+    {file = "psutil-6.1.0-cp36-abi3-macosx_11_0_arm64.whl", hash = "sha256:0895b8414afafc526712c498bd9de2b063deaac4021a3b3c34566283464aff8e"},
+    {file = "psutil-6.1.0-cp36-abi3-manylinux_2_12_i686.manylinux2010_i686.manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:9dcbfce5d89f1d1f2546a2090f4fcf87c7f669d1d90aacb7d7582addece9fb38"},
+    {file = "psutil-6.1.0-cp36-abi3-manylinux_2_12_x86_64.manylinux2010_x86_64.manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:498c6979f9c6637ebc3a73b3f87f9eb1ec24e1ce53a7c5173b8508981614a90b"},
+    {file = "psutil-6.1.0-cp36-abi3-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:d905186d647b16755a800e7263d43df08b790d709d575105d419f8b6ef65423a"},
+    {file = "psutil-6.1.0-cp36-cp36m-win32.whl", hash = "sha256:6d3fbbc8d23fcdcb500d2c9f94e07b1342df8ed71b948a2649b5cb060a7c94ca"},
+    {file = "psutil-6.1.0-cp36-cp36m-win_amd64.whl", hash = "sha256:1209036fbd0421afde505a4879dee3b2fd7b1e14fee81c0069807adcbbcca747"},
+    {file = "psutil-6.1.0-cp37-abi3-win32.whl", hash = "sha256:1ad45a1f5d0b608253b11508f80940985d1d0c8f6111b5cb637533a0e6ddc13e"},
+    {file = "psutil-6.1.0-cp37-abi3-win_amd64.whl", hash = "sha256:a8fb3752b491d246034fa4d279ff076501588ce8cbcdbb62c32fd7a377d996be"},
+    {file = "psutil-6.1.0.tar.gz", hash = "sha256:353815f59a7f64cdaca1c0307ee13558a0512f6db064e92fe833784f08539c7a"},
+]
+
+[package.extras]
+dev = ["black", "check-manifest", "coverage", "packaging", "pylint", "pyperf", "pypinfo", "pytest-cov", "requests", "rstcheck", "ruff", "sphinx", "sphinx_rtd_theme", "toml-sort", "twine", "virtualenv", "wheel"]
+test = ["pytest", "pytest-xdist", "setuptools"]
+
 [[package]]
 name = "xeger"
 version = "0.4.0"
@@ -38,4 +68,4 @@ files = [
 [metadata]
 lock-version = "2.0"
 python-versions = ">=3.6"
-content-hash = "f61b42d8bd0c6814638b0f4d9b5afa1b049f7ab03fb55dbdceaceba39936d21c"
+content-hash = "3b7d7552aab0b4bfb77c96178a91816d9a53ba6eda49c7bd46f008583f7c3ae0"
diff --git a/pyproject.toml b/pyproject.toml
index 59ae302..6c8b023 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,6 +10,7 @@ readme = "README.md"
 python = ">=3.6"
 xeger = "^0.4.0"
 colorful = "^0.5.6"
+psutil = "^6.1.0"
 
 
 [build-system]