diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index dd27dea4f0d97..e8c2d325bd653 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::cell::RefCell;
 use std::collections::BTreeMap;
 use std::env;
 
@@ -31,12 +30,6 @@ pub use errors::*;
 // Maximum width of any line in an extended error description (inclusive).
 const MAX_DESCRIPTION_WIDTH: usize = 80;
 
-thread_local! {
-    static REGISTERED_DIAGNOSTICS: RefCell<ErrorMap> = {
-        RefCell::new(BTreeMap::new())
-    }
-}
-
 /// Error information type.
 pub struct ErrorInfo {
     pub description: Option<Name>,
@@ -46,14 +39,6 @@ pub struct ErrorInfo {
 /// Mapping from error codes to metadata.
 pub type ErrorMap = BTreeMap<Name, ErrorInfo>;
 
-fn with_registered_diagnostics<T, F>(f: F) -> T where
-    F: FnOnce(&mut ErrorMap) -> T,
-{
-    REGISTERED_DIAGNOSTICS.with(move |slot| {
-        f(&mut *slot.borrow_mut())
-    })
-}
-
 pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt,
                                    span: Span,
                                    token_tree: &[TokenTree])
@@ -63,7 +48,7 @@ pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt,
         _ => unreachable!()
     };
 
-    with_registered_diagnostics(|diagnostics| {
+    ecx.parse_sess.registered_diagnostics.with_lock(|diagnostics| {
         match diagnostics.get_mut(&code.name) {
             // Previously used errors.
             Some(&mut ErrorInfo { description: _, use_site: Some(previous_span) }) => {
@@ -132,7 +117,7 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
         }
     });
     // Add the error to the map.
-    with_registered_diagnostics(|diagnostics| {
+    ecx.parse_sess.registered_diagnostics.with_lock(|diagnostics| {
         let info = ErrorInfo {
             description,
             use_site: None
@@ -174,7 +159,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
 
     // Output error metadata to `tmp/extended-errors/<target arch>/<crate name>.json`
     if let Ok(target_triple) = env::var("CFG_COMPILER_HOST_TRIPLE") {
-        with_registered_diagnostics(|diagnostics| {
+        ecx.parse_sess.registered_diagnostics.with_lock(|diagnostics| {
             if let Err(e) = output_metadata(ecx,
                                             &target_triple,
                                             &crate_name.name.as_str(),
@@ -194,7 +179,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
 
     // Construct the output expression.
     let (count, expr) =
-        with_registered_diagnostics(|diagnostics| {
+        ecx.parse_sess.registered_diagnostics.with_lock(|diagnostics| {
             let descriptions: Vec<P<ast::Expr>> =
                 diagnostics.iter().filter_map(|(&code, info)| {
                     info.description.map(|description| {
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 94195ccc72c49..cdf38453d7ea4 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -1764,6 +1764,8 @@ mod tests {
     use std::collections::HashSet;
     use std::io;
     use std::path::PathBuf;
+    use diagnostics::plugin::ErrorMap;
+    use rustc_data_structures::sync::Lock;
     fn mk_sess(cm: Lrc<CodeMap>) -> ParseSess {
         let emitter = errors::emitter::EmitterWriter::new(Box::new(io::sink()),
                                                           Some(cm.clone()),
@@ -1776,6 +1778,7 @@ mod tests {
             included_mod_stack: RefCell::new(Vec::new()),
             code_map: cm,
             missing_fragment_specifiers: RefCell::new(HashSet::new()),
+            registered_diagnostics: Lock::new(ErrorMap::new()),
             non_modrs_mods: RefCell::new(vec![]),
         }
     }
diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index 1d9af682fec8a..3fb0c209f70f4 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -10,7 +10,7 @@
 
 //! The main parser interface
 
-use rustc_data_structures::sync::Lrc;
+use rustc_data_structures::sync::{Lrc, Lock};
 use ast::{self, CrateConfig};
 use codemap::{CodeMap, FilePathMapping};
 use syntax_pos::{self, Span, FileMap, NO_EXPANSION, FileName};
@@ -21,6 +21,7 @@ use ptr::P;
 use str::char_at;
 use symbol::Symbol;
 use tokenstream::{TokenStream, TokenTree};
+use diagnostics::plugin::ErrorMap;
 
 use std::cell::RefCell;
 use std::collections::HashSet;
@@ -47,6 +48,8 @@ pub struct ParseSess {
     pub unstable_features: UnstableFeatures,
     pub config: CrateConfig,
     pub missing_fragment_specifiers: RefCell<HashSet<Span>>,
+    /// The registered diagnostics codes
+    pub registered_diagnostics: Lock<ErrorMap>,
     // Spans where a `mod foo;` statement was included in a non-mod.rs file.
     // These are used to issue errors if the non_modrs_mods feature is not enabled.
     pub non_modrs_mods: RefCell<Vec<(ast::Ident, Span)>>,
@@ -71,6 +74,7 @@ impl ParseSess {
             unstable_features: UnstableFeatures::from_environment(),
             config: HashSet::new(),
             missing_fragment_specifiers: RefCell::new(HashSet::new()),
+            registered_diagnostics: Lock::new(ErrorMap::new()),
             included_mod_stack: RefCell::new(vec![]),
             code_map,
             non_modrs_mods: RefCell::new(vec![]),