diff --git a/tracing-core/Cargo.toml b/tracing-core/Cargo.toml
index 03663ae1b..e4f1bed1c 100644
--- a/tracing-core/Cargo.toml
+++ b/tracing-core/Cargo.toml
@@ -27,7 +27,7 @@ edition = "2018"
 rust-version = "1.63.0"
 
 [features]
-default = ["std", "valuable/std"]
+default = ["std", "valuable?/std"]
 std = ["once_cell"]
 
 [badges]