diff --git a/library/core/src/fmt/rt.rs b/library/core/src/fmt/rt.rs
index 8498f5f5a7c..0596f6c30ce 100644
--- a/library/core/src/fmt/rt.rs
+++ b/library/core/src/fmt/rt.rs
@@ -54,7 +54,7 @@ pub enum Count {
 
 // This needs to match the order of flags in compiler/rustc_ast_lowering/src/format.rs.
 #[derive(Copy, Clone)]
-pub enum Flag {
+pub(super) enum Flag {
     SignPlus,
     SignMinus,
     Alternate,