diff --git a/src/bootstrap/bootstrap_test.py b/src/bootstrap/bootstrap_test.py
index 6da410ed2f279..706f2c5bf0701 100644
--- a/src/bootstrap/bootstrap_test.py
+++ b/src/bootstrap/bootstrap_test.py
@@ -138,6 +138,25 @@ def build_args(self, configure_args=None, args=None, env=None):
         if env is None:
             env = {}
 
+        # This test ends up invoking build_bootstrap_cmd, which searches for
+        # the Cargo binary and errors out if it cannot be found. This is not a
+        # problem in most cases, but there is a scenario where it would cause
+        # the test to fail.
+        #
+        # When a custom local Cargo is configured in config.toml (with the
+        # build.cargo setting), no Cargo is downloaded to any location known by
+        # bootstrap, and bootstrap relies on that setting to find it.
+        #
+        # In this test though we are not using the config.toml of the caller:
+        # we are generating a blank one instead. If we don't set build.cargo in
+        # it, the test will have no way to find Cargo, failing the test.
+        cargo_bin = os.environ.get("BOOTSTRAP_TEST_CARGO_BIN")
+        if cargo_bin is not None:
+            configure_args += ["--set", "build.cargo=" + cargo_bin]
+        rustc_bin = os.environ.get("BOOTSTRAP_TEST_RUSTC_BIN")
+        if rustc_bin is not None:
+            configure_args += ["--set", "build.rustc=" + rustc_bin]
+
         env = env.copy()
         env["PATH"] = os.environ["PATH"]
 
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index 7556a19c90ca0..e08fc3bb1ec63 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -3040,6 +3040,8 @@ impl Step for Bootstrap {
             .args(["-m", "unittest", "bootstrap_test.py"])
             .env("BUILD_DIR", &builder.out)
             .env("BUILD_PLATFORM", builder.build.build.triple)
+            .env("BOOTSTRAP_TEST_RUSTC_BIN", &builder.initial_rustc)
+            .env("BOOTSTRAP_TEST_CARGO_BIN", &builder.initial_cargo)
             .current_dir(builder.src.join("src/bootstrap/"));
         // NOTE: we intentionally don't pass test_args here because the args for unittest and cargo test are mutually incompatible.
         // Use `python -m unittest` manually if you want to pass arguments.
diff --git a/src/bootstrap/src/core/config/config.rs b/src/bootstrap/src/core/config/config.rs
index 36b44d0169c9c..6664c5b451c87 100644
--- a/src/bootstrap/src/core/config/config.rs
+++ b/src/bootstrap/src/core/config/config.rs
@@ -1189,7 +1189,19 @@ impl Config {
     pub fn parse(args: &[String]) -> Config {
         #[cfg(test)]
         fn get_toml(_: &Path) -> TomlConfig {
-            TomlConfig::default()
+            let mut default = TomlConfig::default();
+
+            // When configuring bootstrap for tests, make sure to set the rustc and Cargo to the
+            // same ones used to call the tests. If we don't do that, bootstrap will use its own
+            // detection logic to find a suitable rustc and Cargo, which doesn't work when the
+            // caller is specìfying a custom local rustc or Cargo in their config.toml.
+            default.build = Some(Build {
+                rustc: std::env::var_os("RUSTC").map(|v| v.into()),
+                cargo: std::env::var_os("CARGO").map(|v| v.into()),
+                ..Build::default()
+            });
+
+            default
         }
 
         #[cfg(not(test))]