diff --git a/tracing-subscriber/Cargo.toml b/tracing-subscriber/Cargo.toml
index 0b3da12788..dcea8dcb82 100644
--- a/tracing-subscriber/Cargo.toml
+++ b/tracing-subscriber/Cargo.toml
@@ -26,10 +26,10 @@ keywords = ["logging", "tracing", "metrics", "subscriber"]
 default = ["smallvec", "fmt", "ansi", "tracing-log", "std"]
 alloc = []
 std = ["alloc", "tracing-core/std"]
-env-filter = ["matchers", "regex", "lazy_static", "tracing"]
-fmt = ["registry"]
+env-filter = ["matchers", "regex", "lazy_static", "tracing", "std"]
+fmt = ["registry", "std"]
 ansi = ["fmt", "ansi_term"]
-registry = ["sharded-slab", "thread_local"]
+registry = ["sharded-slab", "thread_local", "std"]
 json = ["tracing-serde", "serde", "serde_json"]
 # Enables support for local time when using the `time` crate timestamp
 # formatters.
diff --git a/tracing-subscriber/src/lib.rs b/tracing-subscriber/src/lib.rs
index 730fc05f36..209045283e 100644
--- a/tracing-subscriber/src/lib.rs
+++ b/tracing-subscriber/src/lib.rs
@@ -50,15 +50,16 @@
 //!   (enabled by default).
 //! - `alloc`: Depend on [`liballoc`] (enabled by "std").
 //! - `env-filter`: Enables the [`EnvFilter`] type, which implements filtering
-//!   similar to the [`env_logger` crate].
+//!   similar to the [`env_logger` crate]. **Requires "std"**.
 //! - `fmt`: Enables the [`fmt`] module, which provides a subscriber
 //!   implementation for printing formatted representations of trace events.
-//!   Enabled by default.
+//!   Enabled by default. **Requires "std"**.
 //! - `ansi`: Enables `fmt` support for ANSI terminal colors. Enabled by
 //!   default.
 //! - `registry`: enables the [`registry`] module. Enabled by default.
+//!   **Requires "std"**.
 //! - `json`: Enables `fmt` support for JSON output. In JSON output, the ANSI
-//!   feature does nothing.
+//!   feature does nothing. **Requires "fmt" and "std"**.
 //! - [`local-time`]: Enables local time formatting when using the [`time`
 //!   crate]'s timestamp formatters with the `fmt` subscriber.
 //!