diff --git a/etc/taskcluster/decision_task.py b/etc/taskcluster/decision_task.py
index b67defe5c46b..8b39939373cb 100644
--- a/etc/taskcluster/decision_task.py
+++ b/etc/taskcluster/decision_task.py
@@ -57,7 +57,7 @@ def tasks(task_for):
 
             "try-mac": [macos_unit],
             "try-linux": [linux_tidy_unit, linux_docs_check, linux_release],
-            "try-windows": [windows_unit, windows_arm64, windows_uwp_x64],
+            "try-windows": [windows_arm64, windows_uwp_x64],
             "try-arm": [windows_arm64],
             "try-wpt": [linux_wpt],
             "try-wpt-2020": [linux_wpt_layout_2020],
@@ -319,7 +319,7 @@ def windows_arm64(rdp=False):
         .with_scopes("secrets:get:project/servo/windows-codesign-cert/latest")
         .with_script(
             "python mach build --dev --target=aarch64-uwp-windows-msvc",
-            "python mach package --dev --target aarch64-uwp-windows-msvc --uwp=arm64",
+            "python mach package --dev --target aarch64-uwp-windows-msvc --uwp=ARM64",
         )
         .with_artifacts(appx_artifact)
         .find_or_create("build.windows_uwp_arm64_dev." + CONFIG.tree_hash())
@@ -354,7 +354,7 @@ def uwp_nightly(rdp=False):
         .with_script(
             "python mach build --release --target=x86_64-uwp-windows-msvc",
             "python mach build --release --target=aarch64-uwp-windows-msvc",
-            "mach package --release --target=x86_64-uwp-windows-msvc --uwp=x64 --uwp=arm64",
+            "mach package --release --target=x86_64-uwp-windows-msvc --uwp=x64 --uwp=ARM64",
             "mach upload-nightly uwp --secret-from-taskcluster",
         )
         .with_artifacts(appx_artifact)
diff --git a/python/servo/package_commands.py b/python/servo/package_commands.py
index 5f27a6a63916..35437f5ba9e7 100644
--- a/python/servo/package_commands.py
+++ b/python/servo/package_commands.py
@@ -791,7 +791,7 @@ def run_powershell_cmd(cmd):
 
 
 def build_uwp(platforms, dev, msbuild_dir, ms_app_store):
-    if any(map(lambda p: p not in ['x64', 'x86', 'arm64'], platforms)):
+    if any(map(lambda p: p not in ['x64', 'x86', 'ARM64'], platforms)):
         raise Exception("Unsupported appx platforms: " + str(platforms))
     if dev and len(platforms) > 1:
         raise Exception("Debug package with multiple architectures is unsupported")