diff --git a/Dockerfile b/Dockerfile
index 3fed387f..14e23f03 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1.4
-FROM buildpack-deps:buster as builder-nsjail
+FROM buildpack-deps:bookworm as builder-nsjail
 
 WORKDIR /nsjail
 
@@ -17,7 +17,7 @@ RUN git clone -b master --single-branch https://github.com/google/nsjail.git . \
 RUN make
 
 # ------------------------------------------------------------------------------
-FROM buildpack-deps:buster as builder-py-base
+FROM buildpack-deps:bookworm as builder-py-base
 
 ENV PYENV_ROOT=/pyenv \
     PYTHON_CONFIGURE_OPTS='--disable-test-modules --enable-optimizations \
@@ -42,7 +42,7 @@ RUN git clone -b v2.3.26 --depth 1 https://github.com/pyenv/pyenv.git $PYENV_ROO
     && /build_python.sh 3.12.0rc2
 
 # ------------------------------------------------------------------------------
-FROM python:3.11-slim-buster as base
+FROM python:3.11-slim-bookworm as base
 
 ENV PIP_DISABLE_PIP_VERSION_CHECK=1 \
     PIP_NO_CACHE_DIR=false
@@ -52,7 +52,7 @@ RUN apt-get -y update \
         gcc \
         git \
         libnl-route-3-200 \
-        libprotobuf17 \
+        libprotobuf32 \
     && rm -rf /var/lib/apt/lists/*
 
 COPY --link --from=builder-nsjail /nsjail/nsjail /usr/sbin/
diff --git a/docker-compose.yml b/docker-compose.yml
index 0613abc6..b28d61bc 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -10,7 +10,7 @@ services:
     ports:
      - "8060:8060"
     init: true
-    ipc: none
+    ipc: private
     tty: true
     environment:
       SNEKBOX_DEBUG: 1
diff --git a/snekbox/nsjail.py b/snekbox/nsjail.py
index 1de7b1e7..9bf20bf9 100644
--- a/snekbox/nsjail.py
+++ b/snekbox/nsjail.py
@@ -3,6 +3,7 @@
 import subprocess
 import sys
 from collections.abc import Generator
+from contextlib import nullcontext
 from pathlib import Path
 from tempfile import NamedTemporaryFile
 from typing import Iterable, TypeVar
@@ -56,7 +57,7 @@ def __init__(
         memfs_home: str = "home",
         memfs_output: str = "home",
         files_limit: int | None = 100,
-        files_timeout: int | None = 5,
+        files_timeout: float | None = 5,
         files_pattern: str = "**/[!_]*",
     ):
         """
@@ -267,7 +268,7 @@ def python3(
 
             # Parse attachments with time limit
             try:
-                with time_limit(self.files_timeout):
+                with time_limit(self.files_timeout) if self.files_timeout else nullcontext():
                     attachments = fs.files_list(
                         limit=self.files_limit,
                         pattern=self.files_pattern,
diff --git a/snekbox/utils/timed.py b/snekbox/utils/timed.py
index 11d126c1..59a4e7f4 100644
--- a/snekbox/utils/timed.py
+++ b/snekbox/utils/timed.py
@@ -11,7 +11,7 @@
 
 
 @contextmanager
-def time_limit(timeout: int | None = None) -> Generator[None, None, None]:
+def time_limit(timeout: float) -> Generator[None, None, None]:
     """
     Decorator to call a function with a time limit.
 
@@ -25,10 +25,12 @@ def time_limit(timeout: int | None = None) -> Generator[None, None, None]:
     def signal_handler(_signum, _frame):
         raise TimeoutError(f"time_limit call timed out after {timeout} seconds.")
 
+    # ITIMER_PROF would be more appropriate, but SIGPROF doesn't seem to interrupt sleeps.
     signal.signal(signal.SIGALRM, signal_handler)
-    signal.alarm(timeout)
+    signal.setitimer(signal.ITIMER_REAL, timeout)
 
     try:
         yield
     finally:
-        signal.alarm(0)
+        # Clear the timer if the function finishes early.
+        signal.setitimer(signal.ITIMER_REAL, 0)
diff --git a/tests/test_nsjail.py b/tests/test_nsjail.py
index fe55290f..5d927c26 100644
--- a/tests/test_nsjail.py
+++ b/tests/test_nsjail.py
@@ -233,7 +233,7 @@ def test_file_parsing_timeout(self):
             size = 32 * 1024 * 1024
 
             with open("file", "w") as f:
-                for _ in range((size // 1024) - 5):
+                for _ in range(size // 1024):
                     f.write(data)
 
             for i in range(100):
@@ -242,7 +242,7 @@ def test_file_parsing_timeout(self):
         ).strip()
         # A value higher than the actual memory needed is used to avoid the limit
         # on total file size being reached before the timeout when reading.
-        nsjail = NsJail(memfs_instance_size=512 * Size.MiB, files_timeout=1)
+        nsjail = NsJail(memfs_instance_size=128 * Size.MiB, files_timeout=0.1)
         result = nsjail.python3(["-c", code])
         self.assertEqual(result.returncode, None)
         self.assertEqual(