diff --git a/runtime/src/debug_server.c b/runtime/src/debug_server.c
index abca84bd..8ea0a0b9 100644
--- a/runtime/src/debug_server.c
+++ b/runtime/src/debug_server.c
@@ -16972,7 +16972,23 @@ void debug_server_init(int port)
 #endif
 
     int yes = 1;
+#ifdef _WIN32
+    /* Winsock SO_REUSEADDR permits two listeners on one address/port, with
+     * indeterminate routing. Parallel QA commands must reach exactly one
+     * runtime. Exclusive ownership also refuses an already occupied port.
+     * https://learn.microsoft.com/windows/win32/winsock/so-exclusiveaddruse */
+    if (setsockopt(s_listen, SOL_SOCKET, SO_EXCLUSIVEADDRUSE,
+                   (const char *)&yes, sizeof(yes)) != 0) {
+        s_listen_err = sock_error();
+        fprintf(stdout, "psxrecomp: debug server exclusive socket option FAILED (%d)\n",
+                s_listen_err);
+        sock_close(s_listen);
+        s_listen = SOCK_INVALID;
+        return;
+    }
+#else
     setsockopt(s_listen, SOL_SOCKET, SO_REUSEADDR, (const char *)&yes, sizeof(yes));
+#endif
 
     struct sockaddr_in addr;
     memset(&addr, 0, sizeof(addr));
diff --git a/runtime/tests/check_debug_port_exclusivity.py b/runtime/tests/check_debug_port_exclusivity.py
new file mode 100644
index 00000000..2632190f
--- /dev/null
+++ b/runtime/tests/check_debug_port_exclusivity.py
@@ -0,0 +1,97 @@
+"""Windows integration gate using real hidden runtime processes.
+
+Provide a disposable working directory/config and explicit BIOS/disc. Neither
+the title's release tree nor real memory cards are used. Logs are retained in
+--output; child processes are always stopped by their owned process handles.
+"""
+import argparse
+import json
+import os
+from pathlib import Path
+import socket
+import subprocess
+import time
+
+p=argparse.ArgumentParser()
+for name in ('exe','bios','disc','workdir','output'):
+    p.add_argument('--'+name,type=Path,required=True)
+a=p.parse_args()
+for name in ('exe','bios','disc','workdir','output'):
+    setattr(a,name,getattr(a,name).resolve())
+if os.name != 'nt':
+    raise SystemExit('This integration gate targets Winsock on Windows.')
+a.output.mkdir(parents=True,exist_ok=True)
+children=[]
+streams=[]
+result={}
+def launch(name,port):
+    out=a.output/(name+'.stdout.log'); err=a.output/(name+'.stderr.log')
+    stdout=out.open('wb'); stderr=err.open('wb'); streams.extend((stdout,stderr))
+    cards=a.output/(name+'-cards'); cards.mkdir(exist_ok=True)
+    env=dict(os.environ,SDL_AUDIODRIVER='dummy',PSX_OVERLAY_AUTOCOMPILE_OFF='1')
+    child=subprocess.Popen([str(a.exe),'--headless','--no-launcher','--bios',str(a.bios),
+                            '--disc',str(a.disc),'--memcard-dir',str(cards),
+                            '--debug-port',str(port)],cwd=a.workdir,env=env,
+                           creationflags=subprocess.CREATE_NO_WINDOW,stdout=stdout,stderr=stderr)
+    children.append(child)
+    return child,out
+def wait_log(child,path,needle):
+    end=time.monotonic()+20
+    while time.monotonic()<end:
+        text=path.read_text(errors='replace')
+        if needle in text: return text
+        if child.poll() is not None: raise AssertionError((child.returncode,text))
+        time.sleep(.1)
+    raise TimeoutError((needle,path.read_text(errors='replace')))
+def stop(child):
+    if child.poll() is None:
+        child.terminate(); child.wait(timeout=10)
+def unused_port():
+    with socket.socket() as s:
+        s.bind(('127.0.0.1',0)); return s.getsockname()[1]
+def owners(port):
+    code=f'@(Get-NetTCPConnection -LocalPort {port} -State Listen -ErrorAction SilentlyContinue | Select-Object -ExpandProperty OwningProcess) | ConvertTo-Json -Compress'
+    output=subprocess.check_output(['powershell.exe','-NoProfile','-Command',code],text=True).strip()
+    value=json.loads(output) if output else []
+    return value if isinstance(value,list) else [value]
+
+try:
+    # An existing legacy reusable listener must not be hijacked by this runtime.
+    with socket.socket() as legacy:
+        legacy.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
+        legacy.bind(('127.0.0.1',0)); legacy.listen()
+        port=legacy.getsockname()[1]
+        child,log=launch('occupied-legacy',port)
+        wait_log(child,log,f'debug server bind({port}) FAILED')
+        assert owners(port)==[os.getpid()],owners(port)
+        result['legacy_listener_preserved']=True
+        stop(child)
+
+    port=unused_port()
+    first,log=launch('first',port)
+    wait_log(first,log,f'LISTENING on 127.0.0.1:{port}')
+    assert owners(port)==[first.pid],owners(port)
+    with socket.socket() as competitor:
+        competitor.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
+        try:
+            competitor.bind(('127.0.0.1',port))
+        except OSError as error:
+            assert error.winerror in (10013,10048),error
+            result['reusable_competitor_error']=error.winerror
+        else:
+            raise AssertionError('A competing SO_REUSEADDR bind unexpectedly succeeded')
+    second,log=launch('second',port)
+    wait_log(second,log,f'debug server bind({port}) FAILED')
+    assert owners(port)==[first.pid],owners(port)
+    result['second_runtime_refused']=True
+    stop(second); stop(first)
+    restarted,log=launch('restarted',port)
+    wait_log(restarted,log,f'LISTENING on 127.0.0.1:{port}')
+    assert owners(port)==[restarted.pid],owners(port)
+    result['restart_after_owned_shutdown']=True
+finally:
+    for child in children: stop(child)
+    for stream in streams: stream.close()
+    result['owned_processes_stopped']=all(c.poll() is not None for c in children)
+    (a.output/'result.json').write_text(json.dumps(result,indent=2)+'\n')
+print(json.dumps(result))