diff --git a/src/PostgREST/Middleware.hs b/src/PostgREST/Middleware.hs
index 15380f534c..aeafe53658 100644
--- a/src/PostgREST/Middleware.hs
+++ b/src/PostgREST/Middleware.hs
@@ -128,6 +128,8 @@ corsPolicy req = case lookup "origin" headers of
     headers = Wai.requestHeaders req
     accHeaders = case lookup "access-control-request-headers" headers of
       Just hdrs -> map (CI.mk . BS.strip) $ BS.split ',' hdrs
+       -- Impossible case, Middleware.Cors will not evaluate this when
+       -- the Access-Control-Request-Headers header is not set.
       Nothing   -> []
 
 -- | Set a transaction to eventually roll back if requested and set respective
diff --git a/test/coverage.overlay b/test/coverage.overlay
index e69de29bb2..8583637514 100644
--- a/test/coverage.overlay
+++ b/test/coverage.overlay
@@ -0,0 +1,5 @@
+module "postgrest-9.0.0.20211220-inplace/PostgREST.Middleware" {
+  inside "corsPolicy" {
+    tick "[]" on line 133;
+  }
+}