diff --git a/src/bin/rustfmt.rs b/src/bin/rustfmt.rs
index 1b54d0d4d06..3e369e1ef23 100644
--- a/src/bin/rustfmt.rs
+++ b/src/bin/rustfmt.rs
@@ -79,6 +79,7 @@ fn lookup_and_read_project_file(input_file: &Path) -> io::Result<(PathBuf, Strin
 
 fn update_config(config: &mut Config, matches: &Matches) {
     config.verbose = matches.opt_present("verbose");
+    config.skip_children = matches.opt_present("skip-children");
 }
 
 fn execute() -> i32 {
@@ -90,6 +91,7 @@ fn execute() -> i32 {
                 "write-mode",
                 "mode to write in (not usable when piping from stdin)",
                 "[replace|overwrite|display|diff|coverage]");
+    opts.optflag("", "skip-children", "don't reformat child modules");
 
     opts.optflag("",
                  "config-help",
diff --git a/src/config.rs b/src/config.rs
index 4c919191dbd..804ace83c6d 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -259,6 +259,7 @@ macro_rules! create_config {
 
 create_config! {
     verbose: bool, false, "Use verbose output";
+    skip_children: bool, false, "Don't reformat out of line modules";
     max_width: usize, 100, "Maximum width of each line";
     ideal_width: usize, 80, "Ideal width of each line";
     tab_spaces: usize, 4, "Number of spaces per tab";
diff --git a/src/lib.rs b/src/lib.rs
index 0ee5f71a355..bae42ed44fd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -298,11 +298,15 @@ impl fmt::Display for FormatReport {
 // Formatting which depends on the AST.
 fn fmt_ast(krate: &ast::Crate,
            parse_session: &ParseSess,
+           main_file: &Path,
            config: &Config,
            mode: WriteMode)
            -> FileMap {
     let mut file_map = FileMap::new();
     for (path, module) in modules::list_files(krate, parse_session.codemap()) {
+        if config.skip_children && path.as_path() != main_file {
+            continue;
+        }
         let path = path.to_str().unwrap();
         if config.verbose {
             println!("Formatting {}", path);
@@ -431,7 +435,7 @@ pub fn format(file: &Path, config: &Config, mode: WriteMode) -> FileMap {
     let emitter = Box::new(EmitterWriter::new(Box::new(Vec::new()), None));
     parse_session.span_diagnostic.handler = Handler::with_emitter(false, emitter);
 
-    let mut file_map = fmt_ast(&krate, &parse_session, config, mode);
+    let mut file_map = fmt_ast(&krate, &parse_session, file, config, mode);
 
     // For some reason, the codemap does not include terminating
     // newlines so we must add one on for each file. This is sad.