diff --git a/src/bootstrap/src/core/build_steps/doc.rs b/src/bootstrap/src/core/build_steps/doc.rs
index 75edc8ff78128..dc09d2d109330 100644
--- a/src/bootstrap/src/core/build_steps/doc.rs
+++ b/src/bootstrap/src/core/build_steps/doc.rs
@@ -18,7 +18,7 @@ use crate::core::builder::{
     self, Alias, Builder, Compiler, Kind, RunConfig, ShouldRun, Step, crate_description,
 };
 use crate::core::config::{Config, TargetSelection};
-use crate::helpers::{is_path_in_submodule, symlink_dir, t, up_to_date};
+use crate::helpers::{submodule_path_of, symlink_dir, t, up_to_date};
 
 macro_rules! book {
     ($($name:ident, $path:expr, $book_name:expr, $lang:expr ;)+) => {
@@ -44,8 +44,8 @@ macro_rules! book {
             }
 
             fn run(self, builder: &Builder<'_>) {
-                if is_path_in_submodule(&builder, $path) {
-                    builder.require_submodule($path, None);
+                if let Some(submodule_path) = submodule_path_of(&builder, $path) {
+                    builder.require_submodule(&submodule_path, None)
                 }
 
                 builder.ensure(RustbookSrc {
@@ -933,9 +933,9 @@ macro_rules! tool_doc {
             fn run(self, builder: &Builder<'_>) {
                 let mut source_type = SourceType::InTree;
 
-                if is_path_in_submodule(&builder, $path) {
+                if let Some(submodule_path) = submodule_path_of(&builder, $path) {
                     source_type = SourceType::Submodule;
-                    builder.require_submodule($path, None);
+                    builder.require_submodule(&submodule_path, None);
                 }
 
                 let stage = builder.top_stage;
diff --git a/src/bootstrap/src/utils/helpers.rs b/src/bootstrap/src/utils/helpers.rs
index 2ff99e7e49968..c4780cc56b2d3 100644
--- a/src/bootstrap/src/utils/helpers.rs
+++ b/src/bootstrap/src/utils/helpers.rs
@@ -60,10 +60,12 @@ pub fn is_dylib(path: &Path) -> bool {
     })
 }
 
-/// Returns `true` if the given path is part of a submodule.
-pub fn is_path_in_submodule(builder: &Builder<'_>, path: &str) -> bool {
+/// Return the path to the containing submodule if available.
+pub fn submodule_path_of(builder: &Builder<'_>, path: &str) -> Option<String> {
     let submodule_paths = build_helper::util::parse_gitmodules(&builder.src);
-    submodule_paths.iter().any(|submodule_path| path.starts_with(submodule_path))
+    submodule_paths.iter().find_map(|submodule_path| {
+        if path.starts_with(submodule_path) { Some(submodule_path.to_string()) } else { None }
+    })
 }
 
 fn is_aix_shared_archive(path: &Path) -> bool {
diff --git a/src/bootstrap/src/utils/helpers/tests.rs b/src/bootstrap/src/utils/helpers/tests.rs
index 7bd2a47c63c1c..613286cfaa89a 100644
--- a/src/bootstrap/src/utils/helpers/tests.rs
+++ b/src/bootstrap/src/utils/helpers/tests.rs
@@ -3,8 +3,8 @@ use std::io::Write;
 use std::path::PathBuf;
 
 use crate::utils::helpers::{
-    check_cfg_arg, extract_beta_rev, hex_encode, is_path_in_submodule, make, program_out_of_date,
-    set_file_times, symlink_dir,
+    check_cfg_arg, extract_beta_rev, hex_encode, make, program_out_of_date, set_file_times,
+    submodule_path_of, symlink_dir,
 };
 use crate::{Config, Flags};
 
@@ -117,16 +117,22 @@ fn test_set_file_times_sanity_check() {
 }
 
 #[test]
-fn test_is_path_in_submodule() {
+fn test_submodule_path_of() {
     let config = Config::parse_inner(Flags::parse(&["build".into(), "--dry-run".into()]), |&_| {
         Ok(Default::default())
     });
 
     let build = crate::Build::new(config.clone());
     let builder = crate::core::builder::Builder::new(&build);
-    assert!(!is_path_in_submodule(&builder, "invalid/path"));
-    assert!(is_path_in_submodule(&builder, "src/tools/cargo"));
-    assert!(is_path_in_submodule(&builder, "src/llvm-project"));
+    assert_eq!(submodule_path_of(&builder, "invalid/path"), None);
+    assert_eq!(submodule_path_of(&builder, "src/tools/cargo"), Some("src/tools/cargo".to_string()));
+    assert_eq!(
+        submodule_path_of(&builder, "src/llvm-project"),
+        Some("src/llvm-project".to_string())
+    );
     // Make sure subdirs are handled properly
-    assert!(is_path_in_submodule(&builder, "src/tools/cargo/random-subdir"));
+    assert_eq!(
+        submodule_path_of(&builder, "src/tools/cargo/random-subdir"),
+        Some("src/tools/cargo".to_string())
+    );
 }