diff --git a/Lib/sysconfig/__init__.py b/Lib/sysconfig/__init__.py
index 8ff9c99435bb1a..1f780bc8f44ec0 100644
--- a/Lib/sysconfig/__init__.py
+++ b/Lib/sysconfig/__init__.py
@@ -665,12 +665,17 @@ def get_platform():
 
     For other non-POSIX platforms, currently just returns :data:`sys.platform`."""
     if os.name == 'nt':
+        # Check for architecture in sys.version first, then fall back to sys.maxsize
+        # which is reliable even when sys.version is truncated (e.g., clang builds on Windows)
         if 'amd64' in sys.version.lower():
             return 'win-amd64'
-        if '(arm)' in sys.version.lower():
-            return 'win-arm32'
+        if sys.maxsize > 2**32:
+            # 64-bit Windows where sys.version may be truncated
+            return 'win-amd64'
         if '(arm64)' in sys.version.lower():
             return 'win-arm64'
+        if '(arm)' in sys.version.lower():
+            return 'win-arm32'
         return sys.platform
 
     if os.name != "posix" or not hasattr(os, 'uname'):
diff --git a/Lib/uuid.py b/Lib/uuid.py
index c0150a59d7cb9a..44ab127933876e 100644
--- a/Lib/uuid.py
+++ b/Lib/uuid.py
@@ -951,6 +951,13 @@ def main():
         "@x500": NAMESPACE_X500
     }
 
+    def _namespace_type(value):
+        if value in namespaces:
+            return value
+        # Validate it's a valid UUID string
+        UUID(value)
+        return value
+
     import argparse
     parser = argparse.ArgumentParser(
         formatter_class=argparse.ArgumentDefaultsHelpFormatter,
@@ -962,7 +969,8 @@ def main():
                         default="uuid4",
                         help="function to generate the UUID")
     parser.add_argument("-n", "--namespace",
-                        choices=["any UUID", *namespaces.keys()],
+                        type=_namespace_type,
+                        metavar='{any UUID,@dns,@url,@oid,@x500}',
                         help="uuid3/uuid5 only: "
                         "a UUID, or a well-known predefined UUID addressed "
                         "by namespace name")