diff --git a/cibuildwheel/util.py b/cibuildwheel/util.py
index 4a30aacd..3000ace8 100644
--- a/cibuildwheel/util.py
+++ b/cibuildwheel/util.py
@@ -133,7 +133,7 @@ class Architecture(str, Enum):
 
     # windows archs
     x86 = 'x86'
-    amd64 = 'AMD64'
+    AMD64 = 'AMD64'
 
     @staticmethod
     def parse_config(config: str, platform: str) -> 'List[Architecture]':
@@ -152,7 +152,7 @@ class Architecture(str, Enum):
         if platform == 'linux' and native_architecture == Architecture.x86_64:
             # x86_64 machines can run i686 docker containers
             result.append(Architecture.i686)
-        if platform == 'windows' and native_architecture == Architecture.amd64:
+        if platform == 'windows' and native_architecture == Architecture.AMD64:
             result.append(Architecture.x86)
         return result
 
diff --git a/cibuildwheel/windows.py b/cibuildwheel/windows.py
index a0899fb2..bbd0dfc2 100644
--- a/cibuildwheel/windows.py
+++ b/cibuildwheel/windows.py
@@ -202,7 +202,7 @@ def pep_518_cp35_workaround(package_dir: Path, env: Dict[str, str]) -> None:
 
 
 def build(options: BuildOptions) -> None:
-    if options.architectures != [Architecture.amd64, Architecture.x86]:
+    if options.architectures != [Architecture.AMD64, Architecture.x86]:
         raise ValueError(textwrap.dedent(f'''
             Invalid archs option {options.architectures}. Windows only supports 'amd64,x86' for the
             moment. If you want to set emulation architectures on Linux, use CIBW_ARCHS_LINUX