diff --git a/backend/tests/test_serve_nginx_stop.py b/backend/tests/test_serve_nginx_stop.py
new file mode 100644
index 000000000..b2a6c317e
--- /dev/null
+++ b/backend/tests/test_serve_nginx_stop.py
@@ -0,0 +1,111 @@
+"""Regression coverage for #3758: macOS nginx argv rewriting broke make stop."""
+
+from __future__ import annotations
+
+import shlex
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+SERVE_SH = REPO_ROOT / "scripts" / "serve.sh"
+
+
+def _extract_shell_function(name: str) -> str:
+    text = SERVE_SH.read_text(encoding="utf-8")
+    marker = f"{name}() {{"
+    start = text.index(marker)
+    depth = 0
+    chunks: list[str] = []
+
+    for line in text[start:].splitlines(keepends=True):
+        chunks.append(line)
+        depth += line.count("{") - line.count("}")
+        if depth == 0:
+            return "".join(chunks)
+
+    raise AssertionError(f"Could not extract shell function {name}")
+
+
+def _is_repo_nginx_pid(
+    *,
+    command: str,
+    args: str,
+    repo_root: Path,
+    deerflow_pid: bool = False,
+) -> bool:
+    bash = shutil.which("bash")
+    if bash is None:
+        pytest.skip("bash is required to exercise serve.sh helpers")
+
+    function = _extract_shell_function("_is_repo_nginx_pid")
+    script = f"""
+REPO_ROOT={shlex.quote(str(repo_root))}
+DEERFLOW_ROOTS={shlex.quote(str(repo_root))}
+FAKE_COMMAND={shlex.quote(command)}
+FAKE_ARGS={shlex.quote(args)}
+FAKE_DEERFLOW_PID={1 if deerflow_pid else 0}
+
+_is_deerflow_pid() {{
+    [ "$FAKE_DEERFLOW_PID" = "1" ]
+}}
+
+ps() {{
+    case "$*" in
+        *"-o comm="*) printf '%s\\n' "$FAKE_COMMAND" ;;
+        *"-o args="*) printf '%s\\n' "$FAKE_ARGS" ;;
+        *) return 1 ;;
+    esac
+}}
+
+{function}
+
+_is_repo_nginx_pid 12345
+"""
+    result = subprocess.run([bash, "-c", script], check=False)
+    return result.returncode == 0
+
+
+def test_repo_nginx_pid_accepts_macos_rewritten_master_command(tmp_path):
+    repo_root = tmp_path / "deer-flow"
+    nginx_conf = repo_root / "docker" / "nginx" / "nginx.local.conf"
+
+    assert _is_repo_nginx_pid(
+        command=f"nginx: master process /opt/homebrew/bin/nginx -c {nginx_conf}",
+        args=f"nginx: master process /opt/homebrew/bin/nginx -c {nginx_conf} -p {repo_root}",
+        repo_root=repo_root,
+    )
+
+
+def test_repo_nginx_pid_accepts_macos_rewritten_worker_after_repo_check(tmp_path):
+    repo_root = tmp_path / "deer-flow"
+
+    assert _is_repo_nginx_pid(
+        command="nginx: worker process",
+        args="nginx: worker process",
+        repo_root=repo_root,
+        deerflow_pid=True,
+    )
+
+
+@pytest.mark.parametrize(
+    ("command", "args", "deerflow_pid"),
+    [
+        ("nginx: worker process", "nginx: worker process", False),
+        ("python", "python -m nginx /tmp/deer-flow/docker/nginx/nginx.local.conf", True),
+    ],
+)
+def test_repo_nginx_pid_rejects_unowned_or_non_nginx_processes(
+    tmp_path,
+    command: str,
+    args: str,
+    deerflow_pid: bool,
+):
+    assert not _is_repo_nginx_pid(
+        command=command,
+        args=args,
+        repo_root=tmp_path / "deer-flow",
+        deerflow_pid=deerflow_pid,
+    )
diff --git a/scripts/serve.sh b/scripts/serve.sh
index bc8d58938..ad49deba1 100755
--- a/scripts/serve.sh
+++ b/scripts/serve.sh
@@ -203,8 +203,10 @@ _is_repo_nginx_pid() {
     local args
 
     command=$(ps -p "$pid" -o comm= 2>/dev/null) || return 1
+    # nginx rewrites argv[0] for master/worker processes. On macOS,
+    # `ps -o comm=` can report that rewritten form instead of the binary name.
     case "$command" in
-        nginx|*/nginx) ;;
+        nginx|*/nginx|nginx:*) ;;
         *) return 1 ;;
     esac