diff --git a/main.py b/main.py
index 22ffbd2..137a037 100644
--- a/main.py
+++ b/main.py
@@ -379,9 +379,13 @@ def main() -> int:
 
     try:
         print(f"Waiting for port {args.port} to open...", file=sys.stderr)
-        if not is_port_open("localhost", args.port, timeout=60.0):
+        if not is_port_open("localhost", args.port, timeout=60.0, container=container):
             print("\nContainer logs:", file=sys.stderr)
             print(container.logs().decode("utf-8", errors="replace"), file=sys.stderr)
+            if container.status in ("exited", "dead"):
+                raise RuntimeError(
+                    f"Posit Connect container exited before port {args.port} opened."
+                )
             raise RuntimeError("Posit Connect did not start within 60 seconds.")
 
         print("Waiting for HTTP server to start...", file=sys.stderr)
@@ -420,20 +424,41 @@ def main() -> int:
             container.stop()
 
 
-def is_port_open(host: str, port: int, timeout: float = 30.0) -> bool:
+def is_port_open(
+    host: str,
+    port: int,
+    timeout: float = 30.0,
+    poll_interval: float = 0.25,
+    container=None,
+) -> bool:
     """
-    Check if a TCP port on a given host is open.
+    Wait until a TCP port on a given host accepts connections.
+
+    Retries until the timeout because a published Docker port may not be
+    bound yet right after the container starts.
 
     :param host: Hostname or IP address to check.
     :param port: Port number to check.
-    :param timeout: Timeout in seconds (default 3.0).
-    :return: True if the port is open (accepting connections), False otherwise.
+    :param timeout: Maximum seconds to wait (default 30).
+    :param poll_interval: Seconds between connection attempts (default 0.25).
+    :param container: Optional docker container; stop waiting if it exits.
+    :return: True if the port opened before the timeout, False otherwise.
     """
-    try:
-        with socket.create_connection((host, port), timeout=timeout):
-            return True
-    except (socket.timeout, ConnectionRefusedError, OSError):
-        return False
+    deadline = time.monotonic() + timeout
+    while True:
+        if container is not None:
+            container.reload()
+            if container.status in ("exited", "dead"):
+                return False
+        remaining = deadline - time.monotonic()
+        try:
+            with socket.create_connection((host, port), timeout=max(remaining, 0.1)):
+                return True
+        except (socket.timeout, ConnectionRefusedError, OSError):
+            remaining = deadline - time.monotonic()
+            if remaining <= 0:
+                return False
+            time.sleep(min(poll_interval, remaining))
 
 
 def extract_server_version(logs: str) -> str | None:
diff --git a/test_main.py b/test_main.py
index 41525dc..a3f4529 100644
--- a/test_main.py
+++ b/test_main.py
@@ -170,6 +170,46 @@ def test_extract_server_version_dev():
     assert main.extract_server_version(logs) == "2025.11.0-dev+29-gd0db52662c"
 
 
+def test_is_port_open_retries_until_port_opens():
+    # Docker Desktop refuses connections briefly after the container starts
+    refused = ConnectionRefusedError("Connection refused")
+    with patch.object(
+        main.socket, "create_connection", side_effect=[refused, refused, MagicMock()]
+    ) as create_connection:
+        result = main.is_port_open("localhost", 3939, timeout=5.0, poll_interval=0.01)
+
+    assert result is True
+    assert create_connection.call_count == 3
+
+
+def test_is_port_open_times_out_on_closed_port():
+    # Bind and close a socket to get a port that nothing is listening on
+    with main.socket.socket() as s:
+        s.bind(("localhost", 0))
+        port = s.getsockname()[1]
+
+    start = main.time.monotonic()
+    result = main.is_port_open("localhost", port, timeout=0.5, poll_interval=0.05)
+    elapsed = main.time.monotonic() - start
+
+    assert result is False
+    assert 0.4 <= elapsed < 5.0
+
+
+def test_is_port_open_stops_when_container_exits():
+    mock_container = MagicMock()
+    mock_container.status = "exited"
+
+    with patch.object(main.socket, "create_connection") as create_connection:
+        result = main.is_port_open(
+            "localhost", 3939, timeout=30.0, container=mock_container
+        )
+
+    assert result is False
+    mock_container.reload.assert_called_once()
+    create_connection.assert_not_called()
+
+
 def test_local_image_usage():
     mock_args = Mock()
     mock_args.version = "2024.08.0"
@@ -471,6 +511,15 @@ def test_post_bootstrap_raises_on_other_errors():
     test_extract_server_version_dev()
     print("✓ test_extract_server_version_dev passed")
 
+    test_is_port_open_retries_until_port_opens()
+    print("✓ test_is_port_open_retries_until_port_opens passed")
+
+    test_is_port_open_times_out_on_closed_port()
+    print("✓ test_is_port_open_times_out_on_closed_port passed")
+
+    test_is_port_open_stops_when_container_exits()
+    print("✓ test_is_port_open_stops_when_container_exits passed")
+
     test_local_image_usage()
     print("✓ test_local_image_usage passed")