diff --git a/src/checkstyle.rs b/src/checkstyle.rs
index e25bfc03ba4..02e214864fa 100644
--- a/src/checkstyle.rs
+++ b/src/checkstyle.rs
@@ -8,30 +8,30 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 use rustfmt_diff::{Mismatch, DiffLine};
-use std::io::{self, Write, Read, stdout};
+use std::io::{self, Write, Read};
 use config::WriteMode;
 
 
-pub fn output_header(mode: WriteMode) -> Result<(), io::Error> {
-    let stdout = stdout();
-    let mut stdout = stdout.lock();
+pub fn output_header<T>(out: &mut T, mode: WriteMode) -> Result<(), io::Error>
+    where T: Write
+{
     if mode == WriteMode::Checkstyle {
         let mut xml_heading = String::new();
         xml_heading.push_str("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
         xml_heading.push_str("\n");
         xml_heading.push_str("<checkstyle version=\"4.3\">");
-        try!(write!(stdout, "{}", xml_heading));
+        try!(write!(out, "{}", xml_heading));
     }
     Ok(())
 }
 
-pub fn output_footer(mode: WriteMode) -> Result<(), io::Error> {
-    let stdout = stdout();
-    let mut stdout = stdout.lock();
+pub fn output_footer<T>(out: &mut T, mode: WriteMode) -> Result<(), io::Error>
+    where T: Write
+{
     if mode == WriteMode::Checkstyle {
         let mut xml_tail = String::new();
         xml_tail.push_str("</checkstyle>");
-        try!(write!(stdout, "{}", xml_tail));
+        try!(write!(out, "{}", xml_tail));
     }
     Ok(())
 }
diff --git a/src/filemap.rs b/src/filemap.rs
index dabf7ade3e1..61ad573f702 100644
--- a/src/filemap.rs
+++ b/src/filemap.rs
@@ -31,15 +31,18 @@ pub fn append_newlines(file_map: &mut FileMap) {
     }
 }
 
-pub fn write_all_files(file_map: &FileMap,
-                       mode: WriteMode,
-                       config: &Config)
-                       -> Result<(), io::Error> {
-    output_header(mode).ok();
+pub fn write_all_files<T>(file_map: &FileMap,
+                          mut out: T,
+                          mode: WriteMode,
+                          config: &Config)
+                          -> Result<(), io::Error>
+    where T: Write
+{
+    output_header(&mut out, mode).ok();
     for filename in file_map.keys() {
-        try!(write_file(&file_map[filename], filename, mode, config));
+        try!(write_file(&file_map[filename], filename, &mut out, mode, config));
     }
-    output_footer(mode).ok();
+    output_footer(&mut out, mode).ok();
 
     Ok(())
 }
@@ -81,11 +84,14 @@ pub fn write_system_newlines<T>(writer: T,
     }
 }
 
-pub fn write_file(text: &StringBuffer,
-                  filename: &str,
-                  mode: WriteMode,
-                  config: &Config)
-                  -> Result<Option<String>, io::Error> {
+pub fn write_file<T>(text: &StringBuffer,
+                     filename: &str,
+                     out: &mut T,
+                     mode: WriteMode,
+                     config: &Config)
+                     -> Result<Option<String>, io::Error>
+    where T: Write
+{
 
     fn source_and_formatted_text(text: &StringBuffer,
                                  filename: &str,
@@ -155,11 +161,8 @@ pub fn write_file(text: &StringBuffer,
             unreachable!("The WriteMode should NEVER Be default at this point!");
         }
         WriteMode::Checkstyle => {
-            let stdout = stdout();
-            let stdout = stdout.lock();
             let diff = try!(create_diff(filename, text, config));
-            // Output the XML tags for the lines that are different.
-            try!(output_checkstyle_file(stdout, filename, diff));
+            try!(output_checkstyle_file(out, filename, diff));
         }
     }
 
diff --git a/src/lib.rs b/src/lib.rs
index 6d60c0f278d..ad9322ab649 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -30,6 +30,7 @@ use syntax::codemap::{mk_sp, Span};
 use syntax::diagnostic::{EmitterWriter, Handler};
 use syntax::parse::{self, ParseSess};
 
+use std::io::stdout;
 use std::ops::{Add, Sub};
 use std::path::Path;
 use std::collections::HashMap;
@@ -428,8 +429,8 @@ pub fn run(file: &Path, write_mode: WriteMode, config: &Config) {
     let mut result = format(file, config, mode);
 
     print!("{}", fmt_lines(&mut result, config));
-
-    let write_result = filemap::write_all_files(&result, mode, config);
+    let out = stdout();
+    let write_result = filemap::write_all_files(&result, out, mode, config);
 
     if let Err(msg) = write_result {
         println!("Error writing files: {}", msg);
@@ -442,7 +443,8 @@ pub fn run_from_stdin(input: String, write_mode: WriteMode, config: &Config) {
     let mut result = format_string(input, config, mode);
     fmt_lines(&mut result, config);
 
-    let write_result = filemap::write_file(&result["stdin"], "stdin", mode, config);
+    let mut out = stdout();
+    let write_result = filemap::write_file(&result["stdin"], "stdin", &mut out, mode, config);
 
     if let Err(msg) = write_result {
         panic!("Error writing to stdout: {}", msg);