diff --git a/.buildkite/autogenerate_pipeline.py b/.buildkite/autogenerate_pipeline.py
index ee28b24..c9d1fab 100755
--- a/.buildkite/autogenerate_pipeline.py
+++ b/.buildkite/autogenerate_pipeline.py
@@ -321,10 +321,10 @@ def build(self, input, platform_allowlist):
                 if test_name in tests_to_skip:
                     continue
 
-            # The platform is optional. When it is not specified, we don't add
-            # it to the step so that we can run the test in any environment.
+            # The platform is optional. When it is not specified, it defaults
+            # to `x86_64` to get checked against `platform_allowlist`.
             if not platforms:
-                platforms = [None]
+                platforms = ["x86_64"]
 
             for platform in platforms:
                 # Filter test enabled in platform_allowlist