diff --git a/src/engine/win32/contract.h b/src/engine/win32/contract.h
index 36cb0d9..ed0210c 100644
--- a/src/engine/win32/contract.h
+++ b/src/engine/win32/contract.h
@@ -1,13 +1,14 @@
-#ifndef CONTRACT_MAGIC0
-#define CONTRACT_MAGIC0 0x3A7C1E94B2D6F058ull
+#ifndef CONTRACT_MAGIC
+#define CONTRACT_MAGIC 0x3A7C1E94B2D6F058ull
 #endif
 
-#ifndef CONTRACT_MAGIC1
-#define CONTRACT_MAGIC1 0x9F41D80E6BC57A23ull
-#endif
-
-#ifndef CONTRACT_ACK
-#define CONTRACT_ACK 0xACED5EEDACED5EEDull
+/* Companion magic = byte-reversed primary, folded to an immediate at -O2 (no
+ * runtime bswap). One source of truth; in memory magic0 ++ magic1 forms a
+ * 16-byte palindrome. The host echoes this value into `ack` to acknowledge, so
+ * there is no separate ack constant. (CONTRACT_MAGIC must not be a byte
+ * palindrome, or magic1 would equal magic0.) */
+#ifndef CONTRACT_MAGIC_R
+#define CONTRACT_MAGIC_R (__builtin_bswap64(CONTRACT_MAGIC))
 #endif
 
 #ifndef VMIE_CONTRACT_H
diff --git a/src/engine/win32/guest.c b/src/engine/win32/guest.c
index 7b1851f..e593f61 100644
--- a/src/engine/win32/guest.c
+++ b/src/engine/win32/guest.c
@@ -5,13 +5,8 @@
 #define ACK_POLL_MS    5u
 #endif
 
-#ifndef ACK_TIMEOUT_MS
-#define ACK_TIMEOUT_MS (120*1000u)
-#endif
-
 int main(void) {
     contract* c = VirtualAlloc(NULL, sizeof *c, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
-    uint32_t timeout = ACK_TIMEOUT_MS;
     if (c == NULL) {
         return 1;
     }
@@ -20,22 +15,21 @@ int main(void) {
 
     c->va_self = (uint64_t)(uintptr_t)c;
     c->ack     = 0;
-    c->magic1  = CONTRACT_MAGIC1;
+    c->magic1  = CONTRACT_MAGIC_R;
 
     MemoryBarrier();
-    c->magic0 = CONTRACT_MAGIC0;
+    c->magic0 = CONTRACT_MAGIC;
 
-    do {
-        if (*(volatile uint64_t*)&c->ack == CONTRACT_ACK) {
-            c->magic0 = 0;
-            c->magic1 = 0;
-            VirtualUnlock(c, sizeof *c);
-            VirtualFree(c, 0, MEM_RELEASE);
-            break;
-        }
+    /* Live until acknowledged. A VMI host may attach at any moment - or only
+     * after the guest has idled for a long time - so there is no justified
+     * deadline: poll the ack flag forever, exit only once the host sets it. */
+    while (*(volatile uint64_t*)&c->ack != CONTRACT_MAGIC_R) {
+        Sleep(ACK_POLL_MS);
+    }
 
-       Sleep(ACK_POLL_MS);
-    } while (timeout -= ACK_POLL_MS);
-
-    return timeout > 0 ? 0 : 255;
+    c->magic0 = 0;
+    c->magic1 = 0;
+    VirtualUnlock(c, sizeof *c);
+    VirtualFree(c, 0, MEM_RELEASE);
+    return 0;
 }
\ No newline at end of file
diff --git a/src/engine/win32/host.c b/src/engine/win32/host.c
index 34db062..2f7d02a 100644
--- a/src/engine/win32/host.c
+++ b/src/engine/win32/host.c
@@ -62,7 +62,7 @@ static int beacon_find(vmie_mem* m, uint64_t* pa, uint64_t* va) {
 
     do {
         const contract* c = (void*)ptr;
-        if (c->magic0 == CONTRACT_MAGIC0 && c->magic1 == CONTRACT_MAGIC1) {
+        if (c->magic0 == CONTRACT_MAGIC && c->magic1 == CONTRACT_MAGIC_R) {
             *pa = offset_gpa(m, ptr - m->pa);
             *va = c->va_self;
             return 0;
@@ -204,7 +204,7 @@ static uint32_t ko_export_rva(vmie_mem* m, uintptr_t cr3, uint64_t kbase, const
 }
 
 static void beacon_ack(vmie_mem* m, uint64_t anchor_pa) {
-    uint64_t ack = CONTRACT_ACK;
+    uint64_t ack = CONTRACT_MAGIC_R;
     gpa_write(m, anchor_pa + offsetof(contract, ack), &ack, 8);
 }