diff --git a/libs/opsqueue_python/tests/conftest.py b/libs/opsqueue_python/tests/conftest.py
index b4b10bf..625f722 100644
--- a/libs/opsqueue_python/tests/conftest.py
+++ b/libs/opsqueue_python/tests/conftest.py
@@ -6,6 +6,8 @@
 import subprocess
 import uuid
 import os
+from libs.opsqueue_python.tests.util import wait_for_server
+import psutil
 import pytest
 from dataclasses import dataclass
 from pathlib import Path
@@ -52,13 +54,10 @@ def opsqueue() -> Generator[OpsqueueProcess, None, None]:
 
 @contextmanager
 def opsqueue_service(
-    *, port: int | None = None
+    *, port: int = 0,
 ) -> Generator[OpsqueueProcess, None, None]:
     global test_opsqueue_port_offset
 
-    if port is None:
-        port = random_free_port()
-
     temp_dbname = f"/tmp/opsqueue_tests-{uuid.uuid4()}.db"
 
     command = [
@@ -72,7 +71,8 @@ def opsqueue_service(
     if env.get("RUST_LOG") is None:
         env["RUST_LOG"] = "off"
 
-    with subprocess.Popen(command, cwd=PROJECT_ROOT, env=env) as process:
+    with psutil.Popen(command, cwd=PROJECT_ROOT, env=env) as process:
+        _host, port = wait_for_server(process)
         try:
             wrapper = OpsqueueProcess(port=port, process=process)
             yield wrapper
diff --git a/libs/opsqueue_python/tests/util.py b/libs/opsqueue_python/tests/util.py
new file mode 100644
index 0000000..1b2d76f
--- /dev/null
+++ b/libs/opsqueue_python/tests/util.py
@@ -0,0 +1,57 @@
+import logging
+
+import psutil
+from opnieuw import retry
+from psutil._common import pconn
+
+LOGGER = logging.getLogger(__name__)
+
+
+@retry(
+    retry_on_exceptions=ValueError,
+    max_calls_total=5,
+    retry_window_after_first_call_in_seconds=5,
+)
+def wait_for_server(proc: psutil.Popen) -> tuple[str, int]:
+    """
+    Wait for a process to be listening on a single port.
+    If the process is listening on no ports, a ValueError is thrown and this is retried.
+    If multiple ports are listening, a RuntimeError is thrown.
+    """
+    if not proc.is_running():
+        raise ValueError(f"Process {proc} is not running")
+
+    try:
+        # Try to get the connections of the main process first, if that fails try the children.
+        # Processes wrapped with `timeout` do not have connections themselves.
+        connections: list[pconn] = (
+            proc.net_connections()
+            or [
+                child_conn
+                for child in proc.children(recursive=False)
+                for child_conn in child.net_connections()
+            ]
+            or [
+                child_conn
+                for child in proc.children(recursive=True)
+                for child_conn in child.net_connections()
+            ]
+        )
+    except psutil.AccessDenied as e:
+        match proc.status():
+            case psutil.STATUS_ZOMBIE | psutil.STATUS_DEAD | psutil.STATUS_STOPPED:
+                raise RuntimeError(f"Process {proc} has exited unexpectedly") from e
+            case _:
+                raise RuntimeError(
+                    f"Could not get `net_connections` for process {proc}, access denied "
+                ) from e
+
+    ports = [x for x in connections if x.status == psutil.CONN_LISTEN]
+    listen_count = len(ports)
+
+    if listen_count == 0:
+        raise ValueError(f"Process {proc} is not listening on any ports")
+    if listen_count == 1:
+        return ports[0].laddr
+
+    raise RuntimeError(f"Process {proc} is listening on multiple ports")