diff --git a/compiler/rustc_data_structures/src/sharded.rs b/compiler/rustc_data_structures/src/sharded.rs
index c16b9cbf8b7..9f5c97ae798 100644
--- a/compiler/rustc_data_structures/src/sharded.rs
+++ b/compiler/rustc_data_structures/src/sharded.rs
@@ -46,7 +46,7 @@ pub fn new(mut value: impl FnMut() -> T) -> Self {
     fn mask(&self) -> usize {
         #[cfg(parallel_compiler)]
         {
-            self.mask
+            if SHARDS == 1 { 0 } else { self.mask }
         }
         #[cfg(not(parallel_compiler))]
         {