diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index 4c5a677e5543ece..a77ab09f6fa8f0a 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -523,7 +523,8 @@ _Py_ThreadId(void)
 #elif defined(__MINGW32__) && defined(_M_IX86)
     tid = __readfsdword(24);
 #elif defined(__MINGW32__) && defined(_M_ARM64)
-    tid = __getReg(18);
+    // x18 is the Windows ARM64 platform register and points to the TEB.
+    __asm__ ("mov %0, x18" : "=r" (tid));
 #elif defined(__i386__)
     __asm__("{movl %%gs:0, %0|mov %0, dword ptr gs:[0]}" : "=r" (tid));  // 32-bit always uses GS
 #elif defined(__MACH__) && defined(__x86_64__)
diff --git a/Misc/NEWS.d/next/Windows/2026-09-10-02-00-00.gh-issue-157212.x18TEB.rst b/Misc/NEWS.d/next/Windows/2026-09-10-02-00-00.gh-issue-157212.x18TEB.rst
new file mode 100644
index 000000000000000..8d0970516242f93
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2026-09-10-02-00-00.gh-issue-157212.x18TEB.rst
@@ -0,0 +1,3 @@
+Fix ``_Py_ThreadId()`` compilation on Windows ARM64 with MinGW toolchains,
+where ``__getReg()`` is unavailable. The TEB address is now read directly
+from ``x18``. Patch by Christian Aurich.