diff --git a/.cargo/config.toml b/.cargo/config.toml
index d502b62d..26e283ae 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -7,3 +7,6 @@ r-test = "run --manifest-path ./savvy-cli/Cargo.toml -- test"
 # makes the linker ignore these problems.
 [target.x86_64-pc-windows-msvc]
 rustflags = ["-C", "link-arg=/FORCE:UNRESOLVED"]
+
+[toolchain]
+channel = "nightly"
diff --git a/CHANGELOG.md b/CHANGELOG.md
index bbb790c3..7e1b54ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,12 @@
 
 * `r_print!()` and `r_eprint!()` now can print strings containing `%`.
 
+### Breaking Change
+
+* The notation for `savvy-cli test` is now changed to `#[cfg(feature =
+  "savvy-test")]` from `#[cfg(savvy_test)]`. This is to avoid the upcoming
+  change in Cargo ([ref](https://blog.rust-lang.org/2024/05/06/check-cfg.html)).
+
 ## [v0.6.3] (2024-05-05)
 
 ### New features
diff --git a/Cargo.toml b/Cargo.toml
index c45a8e22..12efe4d6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -33,6 +33,8 @@ altrep = ["savvy-ffi/altrep"]
 # Support logger
 logger = ["log", "env_logger"]
 
+savvy-test = []
+
 [build-dependencies]
 cc = "1"
 
diff --git a/R-package/src/rust/src/lib.rs b/R-package/src/rust/src/lib.rs
index a087f76a..39961b6e 100644
--- a/R-package/src/rust/src/lib.rs
+++ b/R-package/src/rust/src/lib.rs
@@ -409,7 +409,7 @@ fn set_name_external(x: &mut Person, name: &str) -> savvy::Result<()> {
     x.set_name(name)
 }
 
-#[cfg(savvy_test)]
+#[cfg(feature = "savvy-test")]
 mod tests {
     #[test]
     fn test_to_upper() -> savvy::Result<()> {
diff --git a/book/src/test.md b/book/src/test.md
index cc0a1c83..77a21f40 100644
--- a/book/src/test.md
+++ b/book/src/test.md
@@ -52,13 +52,13 @@ pub fn foo() -> savvy::Result<()> {
 
 ### Test module
 
-You can write tests under a module marked with `#[cfg(savvy_test)]` instead of
+You can write tests under a module marked with `#[cfg(feature = "savvy-test")]` instead of
 `#[cfg(test)]`. A `#[test]` function needs to have the return value of
 `savvy::Result<()>`, which is the same convention as `#[savvy]`.
 To check if an SEXP contains the expected data, `assert_eq_r_code` is convenient.
 
 ```rust
-#[cfg(savvy_test)]
+#[cfg(feature = "savvy-test")]
 mod test {
     use savvy::{OwnedIntegerSexp, assert_eq_r_code};
 
@@ -73,6 +73,15 @@ mod test {
 }
 ```
 
+Note that `savvy-test` is just a marker for `savvy-cli`, not a real feature. So,
+in theory, you don't really need this. However, in reality, you probably want to
+add it to the `[features]` section of `Cargo.toml` because otherwise Cargo warns.
+
+```toml
+[features]
+savvy-test = []
+```
+
 To test a function that takes user-supplied SEXPs like `IntegerSexp`, you can
 use `.as_read_only()` to convert from the corresponding `Owned-` type. For
 example, if you have a function `your_fn()` that accepts `IntegerSexp`, you can
@@ -85,7 +94,7 @@ pub fn your_fn(x: IntegerSexp) -> savvy::Result<()> {
     // ...snip...
 }
 
-#[cfg(savvy_test)]
+#[cfg(feature = "savvy-test")]
 mod test {
     use savvy::OwnedIntegerSexp;
 
diff --git a/savvy-bindgen/src/gen/templates/lib_rs b/savvy-bindgen/src/gen/templates/lib_rs
index f137dba4..9b94e3e5 100644
--- a/savvy-bindgen/src/gen/templates/lib_rs
+++ b/savvy-bindgen/src/gen/templates/lib_rs
@@ -95,10 +95,10 @@ mod test1 {
     }
 }
 
-// Tests marked under `#[cfg(savvy_test)]` are run by `savvy-cli test`, which
+// Tests marked under `#[cfg(feature = "savvy-test")]` are run by `savvy-cli test`, which
 // executes the Rust code on a real R session so that you can use R things for
 // testing.
-#[cfg(savvy_test)]
+#[cfg(feature = "savvy-test")]
 mod test1 {
     // The return type must be `savvy::Result<()>`
     #[test]
diff --git a/savvy-bindgen/src/parse_file.rs b/savvy-bindgen/src/parse_file.rs
index 01f8651f..6d1112a2 100644
--- a/savvy-bindgen/src/parse_file.rs
+++ b/savvy-bindgen/src/parse_file.rs
@@ -169,7 +169,7 @@ impl ParsedResult {
                 let is_test_mod = item_mod
                     .attrs
                     .iter()
-                    .any(|attr| attr == &parse_quote!(#[cfg(savvy_test)]));
+                    .any(|attr| attr == &parse_quote!(#[cfg(feature = "savvy-test")]));
 
                 match (&item_mod.content, is_test_mod) {
                     (None, false) => {
@@ -346,10 +346,10 @@ fn transform_test_mod(
 ) -> ParsedTestCase {
     let mut item_mod = item_mod.clone();
 
-    // Remove #[cfg(savvy_test)]
+    // Remove #[cfg(feature = "savvy-test")]
     item_mod
         .attrs
-        .retain(|attr| attr != &parse_quote!(#[cfg(savvy_test)]));
+        .retain(|attr| attr != &parse_quote!(#[cfg(feature = "savvy-test")]));
 
     item_mod.ident = format_ident!("__UNIQUE_PREFIX__mod_{}", item_mod.ident);
 
diff --git a/src/eval.rs b/src/eval.rs
index 51a9033c..1de6124d 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -128,7 +128,7 @@ pub fn assert_eq_r_code<T1: Into<Sexp>, T2: AsRef<str>>(actual: T1, expected: T2
     assert!(is_r_identical(actual, parsed));
 }
 
-#[cfg(savvy_test)]
+#[cfg(feature = "savvy-test")]
 mod test {
     use crate::{IntegerSexp, RealSexp};
 
diff --git a/src/sexp/integer.rs b/src/sexp/integer.rs
index ac0f2db4..89668031 100644
--- a/src/sexp/integer.rs
+++ b/src/sexp/integer.rs
@@ -460,7 +460,7 @@ impl IndexMut<usize> for OwnedIntegerSexp {
     }
 }
 
-#[cfg(savvy_test)]
+#[cfg(feature = "savvy-test")]
 mod test {
     use super::OwnedIntegerSexp;
     use crate::NotAvailableValue;