diff --git a/compiler/rustc_serialize/src/json.rs b/compiler/rustc_serialize/src/json.rs
index 044de8e4e2483..6a39854924122 100644
--- a/compiler/rustc_serialize/src/json.rs
+++ b/compiler/rustc_serialize/src/json.rs
@@ -185,8 +185,6 @@ use self::ParserState::*;
 
 use std::borrow::Cow;
 use std::collections::{BTreeMap, HashMap};
-use std::io;
-use std::io::prelude::*;
 use std::mem::swap;
 use std::num::FpCategory as Fp;
 use std::ops::Index;
@@ -250,7 +248,6 @@ pub enum ErrorCode {
 pub enum ParserError {
     /// msg, line, col
     SyntaxError(ErrorCode, usize, usize),
-    IoError(io::ErrorKind, String),
 }
 
 // Builder and Parser have the same errors.
@@ -329,10 +326,6 @@ impl fmt::Display for ErrorCode {
     }
 }
 
-fn io_error_to_error(io: io::Error) -> ParserError {
-    IoError(io.kind(), io.to_string())
-}
-
 impl fmt::Display for ParserError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // FIXME this should be a nicer error
@@ -2163,21 +2156,6 @@ impl<T: Iterator<Item = char>> Builder<T> {
     }
 }
 
-/// Decodes a json value from an `&mut io::Read`
-pub fn from_reader(rdr: &mut dyn Read) -> Result<Json, BuilderError> {
-    let mut contents = Vec::new();
-    match rdr.read_to_end(&mut contents) {
-        Ok(c) => c,
-        Err(e) => return Err(io_error_to_error(e)),
-    };
-    let s = match str::from_utf8(&contents).ok() {
-        Some(s) => s,
-        _ => return Err(SyntaxError(NotUtf8, 0, 0)),
-    };
-    let mut builder = Builder::new(s.chars());
-    builder.build()
-}
-
 /// Decodes a json value from a string
 pub fn from_str(s: &str) -> Result<Json, BuilderError> {
     let mut builder = Builder::new(s.chars());
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 92ee3fd294bdf..c96c52752d02c 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -2148,8 +2148,8 @@ impl Target {
         use std::fs;
 
         fn load_file(path: &Path) -> Result<(Target, TargetWarnings), String> {
-            let contents = fs::read(path).map_err(|e| e.to_string())?;
-            let obj = json::from_reader(&mut &contents[..]).map_err(|e| e.to_string())?;
+            let contents = fs::read_to_string(path).map_err(|e| e.to_string())?;
+            let obj = json::from_str(&contents).map_err(|e| e.to_string())?;
             Target::from_json(obj)
         }