diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index c9a80b7ddd8..64ef126b79e 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -461,7 +461,8 @@ impl LayoutThread {
             ScaleFactor::new(opts::get().device_pixels_per_px.unwrap_or(1.0)));
 
         let configuration =
-            rayon::Configuration::new().num_threads(layout_threads);
+            rayon::Configuration::new().num_threads(layout_threads)
+                                       .start_handler(|_| thread_state::initialize_layout_worker_thread());
         let parallel_traversal = if layout_threads > 1 {
             Some(rayon::ThreadPool::new(configuration).expect("ThreadPool creation failed"))
         } else {
diff --git a/components/style/gecko/global_style_data.rs b/components/style/gecko/global_style_data.rs
index a4812b95a4f..4a6dcc21805 100644
--- a/components/style/gecko/global_style_data.rs
+++ b/components/style/gecko/global_style_data.rs
@@ -15,6 +15,7 @@ use shared_lock::SharedRwLock;
 use std::cmp;
 use std::env;
 use std::ffi::CString;
+use thread_state;
 
 /// Global style data
 pub struct GlobalStyleData {
@@ -39,6 +40,7 @@ fn thread_name(index: usize) -> String {
 }
 
 fn thread_startup(index: usize) {
+    thread_state::initialize_layout_worker_thread();
     unsafe {
         Gecko_SetJemallocThreadLocalArena(true);
     }
diff --git a/components/style/thread_state.rs b/components/style/thread_state.rs
index ab0672e2503..894cdb4a813 100644
--- a/components/style/thread_state.rs
+++ b/components/style/thread_state.rs
@@ -2,15 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-//! Supports dynamic assertions in debug builds about what sort of thread is
-//! running and what state it's in.
-//!
-//! In release builds, `get` returns 0.  All of the other functions inline
-//! away to nothing.
+//! Supports dynamic assertions in about what sort of thread is running and
+//! what state it's in.
 
 #![deny(missing_docs)]
 
-pub use self::imp::{enter, exit, get, initialize};
+use std::cell::RefCell;
 
 bitflags! {
     /// A thread state flag, used for multiple assertions.
@@ -37,22 +34,12 @@ macro_rules! thread_types ( ( $( $fun:ident = $flag:ident ; )* ) => (
         }
 
         $(
-            #[cfg(debug_assertions)]
             #[allow(missing_docs)]
             pub fn $fun(self) -> bool {
                 self.contains($flag)
             }
-            #[cfg(not(debug_assertions))]
-            #[allow(missing_docs)]
-            pub fn $fun(self) -> bool {
-                true
-            }
         )*
     }
-
-    #[cfg(debug_assertions)]
-    static TYPES: &'static [ThreadState] =
-        &[ $( $flag ),* ];
 ));
 
 thread_types! {
@@ -60,64 +47,49 @@ thread_types! {
     is_layout = LAYOUT;
 }
 
-#[cfg(debug_assertions)]
-mod imp {
-    use std::cell::RefCell;
-    use super::{TYPES, ThreadState};
+thread_local!(static STATE: RefCell<Option<ThreadState>> = RefCell::new(None));
 
-    thread_local!(static STATE: RefCell<Option<ThreadState>> = RefCell::new(None));
-
-    /// Initialize the current thread state.
-    pub fn initialize(x: ThreadState) {
-        STATE.with(|ref k| {
-            if let Some(ref s) = *k.borrow() {
-                panic!("Thread state already initialized as {:?}", s);
-            }
-            *k.borrow_mut() = Some(x);
-        });
-        get(); // check the assertion below
-    }
-
-    /// Get the current thread state.
-    pub fn get() -> ThreadState {
-        let state = STATE.with(|ref k| {
-            match *k.borrow() {
-                // This is one of the layout threads, that use rayon.
-                None => super::LAYOUT | super::IN_WORKER,
-                Some(s) => s,
-            }
-        });
-
-        // Exactly one of the thread type flags should be set.
-        assert_eq!(1, TYPES.iter().filter(|&&ty| state.contains(ty)).count());
-        state
-    }
-
-    /// Enter into a given temporary state. Panics if re-entring.
-    pub fn enter(x: ThreadState) {
-        let state = get();
-        assert!(!state.intersects(x));
-        STATE.with(|ref k| {
-            *k.borrow_mut() = Some(state | x);
-        })
-    }
-
-    /// Exit a given temporary state.
-    pub fn exit(x: ThreadState) {
-        let state = get();
-        assert!(state.contains(x));
-        STATE.with(|ref k| {
-            *k.borrow_mut() = Some(state & !x);
-        })
-    }
+/// Initializes the current thread state.
+pub fn initialize(x: ThreadState) {
+    STATE.with(|ref k| {
+        if let Some(ref s) = *k.borrow() {
+            panic!("Thread state already initialized as {:?}", s);
+        }
+        *k.borrow_mut() = Some(x);
+    });
 }
 
-#[cfg(not(debug_assertions))]
-#[allow(missing_docs)]
-mod imp {
-    use super::ThreadState;
-    #[inline(always)] pub fn initialize(_: ThreadState) { }
-    #[inline(always)] pub fn get() -> ThreadState { ThreadState::empty() }
-    #[inline(always)] pub fn enter(_: ThreadState) { }
-    #[inline(always)] pub fn exit(_: ThreadState) { }
+/// Initializes the current thread as a layout worker thread.
+pub fn initialize_layout_worker_thread() {
+    initialize(LAYOUT | IN_WORKER);
+}
+
+/// Gets the current thread state.
+pub fn get() -> ThreadState {
+    let state = STATE.with(|ref k| {
+        match *k.borrow() {
+            None => ThreadState::empty(), // Unknown thread.
+            Some(s) => s,
+        }
+    });
+
+    state
+}
+
+/// Enters into a given temporary state. Panics if re-entring.
+pub fn enter(x: ThreadState) {
+    let state = get();
+    debug_assert!(!state.intersects(x));
+    STATE.with(|ref k| {
+        *k.borrow_mut() = Some(state | x);
+    })
+}
+
+/// Exits a given temporary state.
+pub fn exit(x: ThreadState) {
+    let state = get();
+    debug_assert!(state.contains(x));
+    STATE.with(|ref k| {
+        *k.borrow_mut() = Some(state & !x);
+    })
 }