diff --git a/Cargo.toml b/Cargo.toml
index 67c7a9d67edc8..fe444de6b2782 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -55,6 +55,7 @@ exclude = [
   "compiler/rustc_codegen_gcc",
   "src/bootstrap",
   "tests/rustdoc-gui",
+  "src/doc/reference/mdbook-spec",
   # HACK(eddyb) This hardcodes the fact that our CI uses `/checkout/obj`.
   "obj",
 ]
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index d888e63275cda..7f7c0100947b7 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -2496,7 +2496,9 @@ impl BookTest {
         let path = builder.src.join(&self.path);
         // Books often have feature-gated example text.
         rustbook_cmd.env("RUSTC_BOOTSTRAP", "1");
-        rustbook_cmd.env("PATH", new_path).arg("test").arg(path);
+        rustbook_cmd.env("PATH", new_path).arg("test").arg(&path);
+        // The reference has a nested `cargo run` in `preprocessor.spec` which uses relative paths.
+        rustbook_cmd.current_dir(&path);
 
         // Books may also need to build dependencies. For example, `TheBook` has
         // code samples which use the `trpl` crate. For the `rustdoc` invocation