diff --git a/pkg/provenance.go b/pkg/provenance.go
index 79109e9..f8649b8 100644
--- a/pkg/provenance.go
+++ b/pkg/provenance.go
@@ -162,7 +162,7 @@ func GenerateProvenance(name, digest, ghContext, command, envs string) ([]byte,
 				},
 				// Non user-controllable environment vars needed to reproduce the build.
 				Environment: map[string]interface{}{
-					"arch":               "amd64", // TODO: Does GitHub run actually expose this?
+					"arch":               os.Getenv("RUNNER_ARCH"),
 					"os":                 os.Getenv("ImageOS"),
 					"github_event_name":  gh.EventName,
 					"github_run_number":  gh.RunNumber,