diff --git a/AGENTS.md b/AGENTS.md
index 8e7640a..866cf5d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -46,6 +46,14 @@ automatically. That's packaging, not a fork.
 - Upstream moved the `v0.2.0` protocol tag (from `9c21d6e` to `1c008bc`)
   after tinclib v0.2.0 shipped. The files are identical; only the history
   was rewritten.
+- **v0.4.1 (branch `win-serial-patch`): PC host fix.** With the calculator
+  plugged straight into a PC, `tinc_init()` gave up after 600 ms, before
+  Windows' usbser was loaded and the PC app had the port open.
+  `tinc_init()` now retries HELLO on `NO_REPLY` until `TINC_DEVICE_WAIT_MS`,
+  and a repeat `tinc_init()` keeps USB up instead of re-enumerating (which
+  made COM9 vanish on every retry). While the calculator is idle nothing
+  answers USB, so the PC's open blocks until the next tinclib call. Whether
+  2 s is enough on a first plug-in is not yet measured.
 - **Real firmware, from a PC:** `make pc-link` builds `tools/pc_link.c`
   (the real `src/`, with srldrvce swapped for Win32 serial) and runs it
   against a board on a COM port. Against the v0.1 firmware on COM5, HELLO,
diff --git a/src/tinc_core.c b/src/tinc_core.c
index e1a0595..5b97a5a 100644
--- a/src/tinc_core.c
+++ b/src/tinc_core.c
@@ -219,25 +219,34 @@ tinc_err_t tinc_init(const tinc_config_t *cfg)
     tinc_err_t setup, err;
     clock_t start;
 
-    tinc_shutdown();
+    if (tinc_g.ready)
+        tinc_abort();
     memset(&tinc_g, 0, sizeof tinc_g);
     tinc_g.cfg = cfg ? *cfg : defaults;
     tinc_parser_init(&tinc_g.parser, tinc_g.frame, sizeof tinc_g.frame);
 
     setup = tinc_takeSetupResult();
 
-    if (usb_Init(on_usb, NULL, srl_GetCDCStandardDescriptors(), USB_DEFAULT_INIT_FLAGS)
-        != USB_SUCCESS) {
-        usb_Cleanup();
-        return setup ? setup : TINC_ERR_NO_DEVICE;
+    /* A retry keeps USB up: tearing it down makes a PC host re-enumerate
+     * the calculator, and its COM port goes away with it. */
+    if (!usb_up) {
+        if (usb_Init(on_usb, NULL, srl_GetCDCStandardDescriptors(),
+                     USB_DEFAULT_INIT_FLAGS) != USB_SUCCESS) {
+            usb_Cleanup();
+            return setup ? setup : TINC_ERR_NO_DEVICE;
+        }
+        usb_up = true;
     }
-    usb_up = true;
 
+    /* A PC host is "connected" as soon as it configures us, but its app
+     * can only open the port while we pump USB events, so keep saying
+     * HELLO until the deadline. */
     start = clock();
-    while (!has_srl && !tinc_elapsed(start, TINC_DEVICE_WAIT_MS))
-        usb_HandleEvents();
-
-    err = has_srl ? hello() : TINC_ERR_NO_DEVICE;
+    do {
+        while (!has_srl && !tinc_elapsed(start, TINC_DEVICE_WAIT_MS))
+            usb_HandleEvents();
+        err = has_srl ? hello() : TINC_ERR_NO_DEVICE;
+    } while (err == TINC_ERR_NO_REPLY && !tinc_elapsed(start, TINC_DEVICE_WAIT_MS));
     tinc_g.ready = err == TINC_OK;
     return setup ? setup : err;
 }
diff --git a/src/tinclib.h b/src/tinclib.h
index fcde907..3b97a59 100644
--- a/src/tinclib.h
+++ b/src/tinclib.h
@@ -41,7 +41,7 @@ extern "C" {
  * X.Y, and the board's firmware must too. PATCH counts library-only releases
  * on the same protocol; reset it to 0 when the protocol submodule moves.
  */
-#define TINC_VERSION_PATCH 0
+#define TINC_VERSION_PATCH 1
 
 #define TINC_STR_(x) #x
 #define TINC_STR(x) TINC_STR_(x)
@@ -57,7 +57,10 @@ extern "C" {
 #define TINC_RX_BUF_SIZE 256
 #endif
 
-/** How long tinc_init() waits for the ESP board to show up on USB. */
+/**
+ * How long tinc_init() waits for the board (or a PC host) to show up on USB
+ * and answer HELLO.
+ */
 #ifndef TINC_DEVICE_WAIT_MS
 #define TINC_DEVICE_WAIT_MS 2000u
 #endif
diff --git a/tests/test_tinclib.c b/tests/test_tinclib.c
index b36d65b..728c014 100644
--- a/tests/test_tinclib.c
+++ b/tests/test_tinclib.c
@@ -331,6 +331,26 @@ static void test_lost_reply_is_not_rerun(void)
     CHECK(strcmp(body, "0123456789") == 0);
 }
 
+/* A PC host answers only once its app has the port open: HELLO keeps
+ * being retried until TINC_DEVICE_WAIT_MS, then gives up. */
+static void test_hello_late_reply(void)
+{
+    unsigned long start, elapsed_ms;
+
+    setup();
+    fake.drop_replies = TINC_RETRY_MAX * 2;
+    CHECK(tinc_init(NULL) == TINC_OK);
+    CHECK(fake.frames_in == TINC_RETRY_MAX * 2 + 1);
+
+    setup();
+    fake.drop_replies = 255;
+    start = fake_now;
+    CHECK(tinc_init(NULL) == TINC_ERR_NO_REPLY);
+    elapsed_ms = (fake_now - start) / 1000;
+    CHECK(elapsed_ms >= TINC_DEVICE_WAIT_MS);
+    CHECK(elapsed_ms < TINC_DEVICE_WAIT_MS + TINC_RETRY_MAX * TINC_REPLY_TIMEOUT_MS + 100);
+}
+
 static void test_board_gone_quiet(void)
 {
     tinc_request_t req = get("http://x/");
@@ -561,6 +581,7 @@ int main(void)
     RUN(test_last_chunk_held_until_read);
     RUN(test_is_active_mid_chunk);
     RUN(test_lost_reply_is_not_rerun);
+    RUN(test_hello_late_reply);
     RUN(test_board_gone_quiet);
     RUN(test_esp_reset_mid_request);
     RUN(test_request_errors);