diff --git a/osbuild/testutil/atomic.py b/osbuild/testutil/atomic.py
new file mode 100644
index 00000000..f48b726b
--- /dev/null
+++ b/osbuild/testutil/atomic.py
@@ -0,0 +1,29 @@
+#!/usr/bin/python3
+"""
+thread/atomic related utilities
+"""
+import threading
+
+
+class AtomicCounter:
+    """ A thread-safe counter """
+
+    def __init__(self, count: int = 0) -> None:
+        self._count = count
+        self._lock = threading.Lock()
+
+    def inc(self) -> None:
+        """ increase the count """
+        with self._lock:
+            self._count += 1
+
+    def dec(self) -> None:
+        """ decrease the count """
+        with self._lock:
+            self._count -= 1
+
+    @property
+    def count(self) -> int:
+        """ get the current count """
+        with self._lock:
+            return self._count
diff --git a/osbuild/testutil/net.py b/osbuild/testutil/net.py
index 02be47b4..d2abb565 100644
--- a/osbuild/testutil/net.py
+++ b/osbuild/testutil/net.py
@@ -7,6 +7,8 @@ import http.server
 import socket
 import threading
 
+from .atomic import AtomicCounter
+
 
 def _get_free_port():
     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
@@ -23,13 +25,13 @@ class DirHTTPServer(http.server.ThreadingHTTPServer):
     def __init__(self, *args, directory=None, simulate_failures=0, **kwargs):
         super().__init__(*args, **kwargs)
         self.directory = directory
-        self.simulate_failures = simulate_failures
-        self.reqs = 0
+        self.simulate_failures = AtomicCounter(simulate_failures)
+        self.reqs = AtomicCounter()
 
     def finish_request(self, request, client_address):
-        self.reqs += 1  # racy on non GIL systems
-        if self.simulate_failures > 0:
-            self.simulate_failures -= 1  # racy on non GIL systems
+        self.reqs.inc()
+        if self.simulate_failures.count > 0:
+            self.simulate_failures.dec()
             SilentHTTPRequestHandler(
                 request, client_address, self, directory="does-not-exists")
             return
diff --git a/sources/test/test_curl_source.py b/sources/test/test_curl_source.py
index 626915db..e6bfd061 100644
--- a/sources/test/test_curl_source.py
+++ b/sources/test/test_curl_source.py
@@ -130,7 +130,7 @@ def test_curl_download_many_with_retry(tmp_path, sources_service):
         sources_service.cache.mkdir()
         sources_service.fetch_all(test_sources)
         # we simulated N failures and we need to fetch K files
-        assert httpd.reqs == simulate_failures + len(test_sources)
+        assert httpd.reqs.count == simulate_failures + len(test_sources)
     # double downloads happend in the expected format
     for chksum in test_sources:
         assert (sources_service.cache / chksum).exists()
@@ -165,5 +165,5 @@ def test_curl_download_many_retries(tmp_path, sources_service):
         with pytest.raises(RuntimeError) as exp:
             sources_service.fetch_all(test_sources)
         # curl will retry 10 times
-        assert httpd.reqs == 10 * len(test_sources)
+        assert httpd.reqs.count == 10 * len(test_sources)
         assert "curl: error downloading http://localhost:" in str(exp.value)
diff --git a/tox.ini b/tox.ini
index 505719c5..18f5e3e5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,7 +28,7 @@ setenv =
     LINTABLES_EXCLUDES = "*.json,*.sh"
     LINTABLES_EXCLUDES_RE = ".*\.json$,.*\.sh"
     TYPEABLES = osbuild
-    TYPEABLES_STRICT = ./osbuild/main_cli.py ./osbuild/util/parsing.py
+    TYPEABLES_STRICT = ./osbuild/main_cli.py ./osbuild/util/parsing.py ./osbuild/testutil/atomic.py
 
 passenv =
     TEST_CATEGORY