diff --git a/Cargo.lock b/Cargo.lock
index c34dd3ba18..8f026590e5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -19,6 +19,7 @@ dependencies = [
  "scopeguard 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "sha2 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempdir 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tempfile 2.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "term 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml 0.1.30 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -600,6 +601,7 @@ dependencies = [
  "tempdir 0.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml 0.1.30 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "wait-timeout 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "winreg 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -727,6 +729,18 @@ dependencies = [
  "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "tempfile"
+version = "2.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc_version 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "term"
 version = "0.4.4"
@@ -866,6 +880,14 @@ name = "vec_map"
 version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "wait-timeout"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "walkdir"
 version = "0.1.5"
diff --git a/Cargo.toml b/Cargo.toml
index d876bd09e2..cb7f60c987 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -40,6 +40,7 @@ term = "0.4.4"
 itertools = "0.4.1"
 time = "0.1.34"
 tempdir = "0.3.4"
+tempfile = "2.1.4"
 libc = "0.2.0"
 rand = "0.3.11"
 scopeguard = "0.1.2"
diff --git a/src/rustup-mock/Cargo.toml b/src/rustup-mock/Cargo.toml
index 974092ef87..ddaddc52b6 100644
--- a/src/rustup-mock/Cargo.toml
+++ b/src/rustup-mock/Cargo.toml
@@ -21,6 +21,7 @@ tar = "0.4.0"
 toml = "0.1.27"
 rustup-utils = { path = "../rustup-utils", version = "0.5.0" }
 sha2 = "0.1.2"
+wait-timeout = "0.1.3"
 
 [target."cfg(windows)".dependencies]
 winapi = "0.2.8"
diff --git a/src/rustup-mock/src/clitools.rs b/src/rustup-mock/src/clitools.rs
index 3074db01dd..469c8f99b9 100644
--- a/src/rustup-mock/src/clitools.rs
+++ b/src/rustup-mock/src/clitools.rs
@@ -3,11 +3,12 @@
 
 use std::path::{PathBuf, Path};
 use std::env;
-use std::process::Command;
+use std::process::{Command, Stdio};
 use std::env::consts::EXE_SUFFIX;
 use std::fs::{self, File};
 use std::io::{self, Read, Write};
 use std::sync::Mutex;
+use std::time::Duration;
 use tempdir::TempDir;
 use {MockInstallerBuilder, MockCommand};
 use dist::{MockDistServer, MockChannel, MockPackage,
@@ -15,6 +16,7 @@ use dist::{MockDistServer, MockChannel, MockPackage,
            ManifestVersion};
 use url::Url;
 use scopeguard;
+use wait_timeout::ChildExt;
 
 /// The configuration used by the tests in this module
 pub struct Config {
@@ -218,6 +220,24 @@ pub fn expect_err_ex(config: &Config, args: &[&str],
     assert!(out.stderr == stderr, format!("err {:?}", args));
 }
 
+pub fn expect_timeout_ok(config: &Config, timeout: Duration, args: &[&str]) {
+    let mut child = cmd(config, args[0], &args[1..])
+        .stdout(Stdio::null())
+        .stderr(Stdio::null())
+        .spawn().unwrap();
+
+    match child.wait_timeout(timeout).unwrap() {
+        Some(status) => {
+            assert!(status.success(), "not ok {:?}", args);
+        }
+        None => {
+            // child hasn't exited yet
+            child.kill().unwrap();
+            panic!("command timed out: {:?}", args);
+        }
+    }
+}
+
 #[derive(Debug)]
 pub struct SanitizedOutput {
     pub ok: bool,
@@ -545,18 +565,10 @@ fn mock_bin(_name: &str, version: &str, version_hash: &str) -> Vec<u8> {
         let ref dest_path = tempdir.path().join(&format!("out{}", EXE_SUFFIX));
 
         // Write the source
-        let ref source = format!(r#"
-            fn main() {{
-                let args: Vec<_> = ::std::env::args().collect();
-                if args.get(1) == Some(&"--version".to_string()) {{
-                    println!("{} ({})");
-                }} else if args.get(1) == Some(&"--empty-arg-test".to_string()) {{
-                    assert!(args.get(2) == Some(&"".to_string()));
-                }} else {{
-                    panic!("bad mock proxy commandline");
-                }}
-            }}
-            "#, EXAMPLE_VERSION, EXAMPLE_VERSION_HASH);
+        let source = include_str!("mock_bin_src.rs")
+            .replace("%EXAMPLE_VERSION%", EXAMPLE_VERSION)
+            .replace("%EXAMPLE_VERSION_HASH%", EXAMPLE_VERSION_HASH);
+
         File::create(source_path).and_then(|mut f| f.write_all(source.as_bytes())).unwrap();
 
         // Create the executable
diff --git a/src/rustup-mock/src/lib.rs b/src/rustup-mock/src/lib.rs
index 3b55a0ddca..cf2fe3914b 100644
--- a/src/rustup-mock/src/lib.rs
+++ b/src/rustup-mock/src/lib.rs
@@ -12,6 +12,7 @@ extern crate tar;
 extern crate toml;
 extern crate rustup_utils;
 extern crate sha2;
+extern crate wait_timeout;
 
 #[cfg(windows)]
 extern crate winapi;
diff --git a/src/rustup-mock/src/mock_bin_src.rs b/src/rustup-mock/src/mock_bin_src.rs
new file mode 100644
index 0000000000..d4728f5485
--- /dev/null
+++ b/src/rustup-mock/src/mock_bin_src.rs
@@ -0,0 +1,19 @@
+use std::io::{self, BufWriter, Write};
+
+fn main() {
+    let args: Vec<_> = ::std::env::args().collect();
+    if args.get(1) == Some(&"--version".to_string()) {
+        println!("%EXAMPLE_VERSION% (%EXAMPLE_VERSION_HASH%)");
+    } else if args.get(1) == Some(&"--empty-arg-test".to_string()) {
+        assert!(args.get(2) == Some(&"".to_string()));
+    } else if args.get(1) == Some(&"--huge-output".to_string()) {
+        let out = io::stderr();
+        let lock = out.lock();
+        let mut buf = BufWriter::new(lock);
+        for _ in 0 .. 10000 {
+            buf.write_all(b"error: a value named `fail` has already been defined in this module [E0428]\n").unwrap();
+        }
+    } else {
+        panic!("bad mock proxy commandline");
+    }
+}
diff --git a/src/rustup/command.rs b/src/rustup/command.rs
index 44492150ef..52119a2687 100644
--- a/src/rustup/command.rs
+++ b/src/rustup/command.rs
@@ -1,10 +1,12 @@
 use std::env;
 use std::ffi::OsStr;
-use std::io::{self, Write, BufRead, BufReader};
+use std::fs::File;
+use std::io::{self, Write, BufRead, BufReader, Seek, SeekFrom};
 use std::path::PathBuf;
 use std::process::{self, Command, Stdio};
 use std::time::Instant;
 use regex::Regex;
+use tempfile::tempfile;
 
 use Cfg;
 use errors::*;
@@ -29,6 +31,18 @@ pub fn run_command_for_dir<S: AsRef<OsStr>>(cmd: Command,
 }
 
 fn telemetry_rustc<S: AsRef<OsStr>>(mut cmd: Command, args: &[S], cfg: &Cfg) -> Result<()> {
+    #[cfg(unix)]
+    fn file_as_stdio(file: &File) -> Stdio {
+        use std::os::unix::io::{AsRawFd, FromRawFd};
+        unsafe { Stdio::from_raw_fd(file.as_raw_fd()) }
+    }
+
+    #[cfg(windows)]
+    fn file_as_stdio(file: &File) -> Stdio {
+        use std::os::windows::io::{AsRawHandle, FromRawHandle};
+        unsafe { Stdio::from_raw_handle(file.as_raw_handle()) }
+    }
+
     let now = Instant::now();
 
     cmd.args(&args[1..]);
@@ -44,15 +58,17 @@ fn telemetry_rustc<S: AsRef<OsStr>>(mut cmd: Command, args: &[S], cfg: &Cfg) ->
         cmd.arg("always");
     }
 
+    let mut cmd_err_file = tempfile().unwrap();
+    let cmd_err_stdio = file_as_stdio(&cmd_err_file);
+
     // FIXME rust-lang/rust#32254. It's not clear to me
     // when and why this is needed.
     let mut cmd = cmd.stdin(Stdio::inherit())
                     .stdout(Stdio::inherit())
-                    .stderr(Stdio::piped())
+                    .stderr(cmd_err_stdio)
                     .spawn()
                     .unwrap();
 
-    let mut buffered_stderr = BufReader::new(cmd.stderr.take().unwrap());
     let status = cmd.wait();
 
     let duration = now.elapsed();
@@ -75,6 +91,10 @@ fn telemetry_rustc<S: AsRef<OsStr>>(mut cmd: Command, args: &[S], cfg: &Cfg) ->
             let stderr = io::stderr();
             let mut handle = stderr.lock();
 
+            cmd_err_file.seek(SeekFrom::Start(0)).unwrap();
+
+            let mut buffered_stderr = BufReader::new(cmd_err_file);
+
             while buffered_stderr.read_line(&mut buffer).unwrap() > 0 {
                 let b = buffer.to_owned();
                 buffer.clear();
diff --git a/src/rustup/lib.rs b/src/rustup/lib.rs
index 0501b2887e..f3dda44699 100644
--- a/src/rustup/lib.rs
+++ b/src/rustup/lib.rs
@@ -9,6 +9,7 @@ extern crate url;
 extern crate regex;
 extern crate itertools;
 extern crate rustc_serialize;
+extern crate tempfile;
 extern crate time;
 extern crate toml;
 #[cfg(unix)]
diff --git a/tests/cli-misc.rs b/tests/cli-misc.rs
index a5bce27b13..ce536f4f9f 100644
--- a/tests/cli-misc.rs
+++ b/tests/cli-misc.rs
@@ -7,13 +7,14 @@ extern crate rustup_mock;
 extern crate time;
 use rustup_mock::clitools::{self, Config, Scenario,
                                expect_stdout_ok, expect_stderr_ok,
-                               expect_ok, expect_err, run,
-                               this_host_triple};
+                               expect_ok, expect_err, expect_timeout_ok,
+                               run, this_host_triple};
 use rustup_utils::{raw, utils};
 
 use time::Duration;
 use std::ops::Sub;
 use std::ops::Add;
+use std::time::Duration as StdDuration;
 
 macro_rules! for_host { ($s: expr) => (&format!($s, this_host_triple())) }
 
@@ -334,6 +335,16 @@ fn enabling_telemetry_and_compiling_creates_log() {
     });
 }
 
+#[test]
+fn telemetry_supports_huge_output() {
+    setup(&|config| {
+        expect_ok(config, &["rustup", "default", "stable"]);
+        expect_ok(config, &["rustup", "telemetry", "enable"]);
+        expect_timeout_ok(&config, StdDuration::from_secs(5), &["rustc", "--huge-output"]);
+        expect_stdout_ok(config, &["rustup", "telemetry", "analyze"], "'E0428': 10000")
+    })
+}
+
 #[test]
 fn telemetry_cleanup_removes_old_files() {
     setup(&|config| {