diff --git a/library/compiler-builtins/libm/Cargo.toml b/library/compiler-builtins/libm/Cargo.toml
index 3e6817851ba7..37aff9a765bb 100644
--- a/library/compiler-builtins/libm/Cargo.toml
+++ b/library/compiler-builtins/libm/Cargo.toml
@@ -11,18 +11,16 @@ version = "0.2.0"
 edition = "2018"
 
 [features]
-# only used to run our test suite
-default = ['stable']
-stable = []
+default = []
+
+# This tells the compiler to assume that a Nightly toolchain is being used and
+# that it should activate any useful Nightly things accordingly.
+unstable = []
 
 # Generate tests which are random inputs and the outputs are calculated with
 # musl libc.
 musl-reference-tests = ['rand']
 
-# Used checked array indexing instead of unchecked array indexing in this
-# library.
-checked = []
-
 [workspace]
 members = [
   "crates/compiler-builtins-smoke-test",