diff --git a/src/librustc/middle/dead.rs b/src/librustc/middle/dead.rs
index abd52624c30d..a0cd231bb704 100644
--- a/src/librustc/middle/dead.rs
+++ b/src/librustc/middle/dead.rs
@@ -408,7 +408,7 @@ fn create_and_seed_worklist<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     }
 
     // Seed entry point
-    if let Some((id, _)) = *tcx.sess.entry_fn.borrow() {
+    if let Some((id, _, _)) = *tcx.sess.entry_fn.borrow() {
         worklist.push(id);
     }
 
diff --git a/src/librustc/middle/entry.rs b/src/librustc/middle/entry.rs
index 37d79f408f3f..ebc796466629 100644
--- a/src/librustc/middle/entry.rs
+++ b/src/librustc/middle/entry.rs
@@ -63,12 +63,13 @@ pub fn find_entry_point(session: &Session,
     });
     if !any_exe {
         // No need to find a main function
+        session.entry_fn.set(None);
         return
     }
 
     // If the user wants no main function at all, then stop here.
     if attr::contains_name(&hir_map.krate().attrs, "no_main") {
-        session.entry_type.set(Some(config::EntryNone));
+        session.entry_fn.set(None);
         return
     }
 
@@ -153,17 +154,15 @@ fn find_item(item: &Item, ctxt: &mut EntryContext, at_root: bool) {
 }
 
 fn configure_main(this: &mut EntryContext, crate_name: &str) {
-    if this.start_fn.is_some() {
-        *this.session.entry_fn.borrow_mut() = this.start_fn;
-        this.session.entry_type.set(Some(config::EntryStart));
-    } else if this.attr_main_fn.is_some() {
-        *this.session.entry_fn.borrow_mut() = this.attr_main_fn;
-        this.session.entry_type.set(Some(config::EntryMain));
-    } else if this.main_fn.is_some() {
-        *this.session.entry_fn.borrow_mut() = this.main_fn;
-        this.session.entry_type.set(Some(config::EntryMain));
+    if let Some((node_id, span)) = this.start_fn {
+        this.session.entry_fn.set(Some((node_id, span, config::EntryStart)));
+    } else if let Some((node_id, span)) = this.attr_main_fn {
+        this.session.entry_fn.set(Some((node_id, span, config::EntryMain)));
+    } else if let Some((node_id, span)) = this.main_fn {
+        this.session.entry_fn.set(Some((node_id, span, config::EntryMain)));
     } else {
         // No main function
+        this.session.entry_fn.set(None);
         let mut err = struct_err!(this.session, E0601,
             "`main` function not found in crate `{}`", crate_name);
         if !this.non_main_fns.is_empty() {
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index a07370e1e42a..afe4442799b2 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -614,13 +614,11 @@ impl Options {
 
 // The type of entry function, so
 // users can have their own entry
-// functions that don't start a
-// scheduler
+// functions
 #[derive(Copy, Clone, PartialEq)]
 pub enum EntryFnType {
     EntryMain,
     EntryStart,
-    EntryNone,
 }
 
 #[derive(Copy, PartialEq, PartialOrd, Clone, Ord, Eq, Hash, Debug)]
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index c084c8684817..97b73fac1a42 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -70,8 +70,7 @@ pub struct Session {
     pub opts: config::Options,
     pub parse_sess: ParseSess,
     /// For a library crate, this is always none
-    pub entry_fn: RefCell<Option<(NodeId, Span)>>,
-    pub entry_type: Cell<Option<config::EntryFnType>>,
+    pub entry_fn: Once<Option<(NodeId, Span, config::EntryFnType)>>,
     pub plugin_registrar_fn: Cell<Option<ast::NodeId>>,
     pub derive_registrar_fn: Cell<Option<ast::NodeId>>,
     pub default_sysroot: Option<PathBuf>,
@@ -1094,8 +1093,7 @@ pub fn build_session_(
         opts: sopts,
         parse_sess: p_s,
         // For a library crate, this is always none
-        entry_fn: RefCell::new(None),
-        entry_type: Cell::new(None),
+        entry_fn: Once::new(),
         plugin_registrar_fn: Cell::new(None),
         derive_registrar_fn: Cell::new(None),
         default_sysroot,
diff --git a/src/librustc_mir/monomorphize/collector.rs b/src/librustc_mir/monomorphize/collector.rs
index 1189da109299..83ef28e4f156 100644
--- a/src/librustc_mir/monomorphize/collector.rs
+++ b/src/librustc_mir/monomorphize/collector.rs
@@ -325,7 +325,7 @@ fn collect_roots<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let mut roots = Vec::new();
 
     {
-        let entry_fn = tcx.sess.entry_fn.borrow().map(|(node_id, _)| {
+        let entry_fn = tcx.sess.entry_fn.borrow().map(|(node_id, _, _)| {
             tcx.hir.local_def_id(node_id)
         });
 
@@ -1038,7 +1038,7 @@ impl<'b, 'a, 'v> RootCollector<'b, 'a, 'v> {
     /// the return type of `main`. This is not needed when
     /// the user writes their own `start` manually.
     fn push_extra_entry_roots(&mut self) {
-        if self.tcx.sess.entry_type.get() != Some(config::EntryMain) {
+        if self.tcx.sess.entry_fn.get().map(|e| e.2) != Some(config::EntryMain) {
             return
         }
 
diff --git a/src/librustc_mir/monomorphize/item.rs b/src/librustc_mir/monomorphize/item.rs
index c2f4359c0082..181751f17770 100644
--- a/src/librustc_mir/monomorphize/item.rs
+++ b/src/librustc_mir/monomorphize/item.rs
@@ -92,7 +92,7 @@ pub trait MonoItemExt<'a, 'tcx>: fmt::Debug {
         match *self.as_mono_item() {
             MonoItem::Fn(ref instance) => {
                 let entry_def_id =
-                    tcx.sess.entry_fn.borrow().map(|(id, _)| tcx.hir.local_def_id(id));
+                    tcx.sess.entry_fn.borrow().map(|(id, _, _)| tcx.hir.local_def_id(id));
                 // If this function isn't inlined or otherwise has explicit
                 // linkage, then we'll be creating a globally shared version.
                 if self.explicit_linkage(tcx).is_some() ||
diff --git a/src/librustc_trans/base.rs b/src/librustc_trans/base.rs
index 0329264a3125..dd51ffcf3136 100644
--- a/src/librustc_trans/base.rs
+++ b/src/librustc_trans/base.rs
@@ -517,7 +517,7 @@ pub fn set_link_section(cx: &CodegenCx,
 /// users main function.
 fn maybe_create_entry_wrapper(cx: &CodegenCx) {
     let (main_def_id, span) = match *cx.sess().entry_fn.borrow() {
-        Some((id, span)) => {
+        Some((id, span, _)) => {
             (cx.tcx.hir.local_def_id(id), span)
         }
         None => return,
@@ -533,11 +533,11 @@ fn maybe_create_entry_wrapper(cx: &CodegenCx) {
 
     let main_llfn = callee::get_fn(cx, instance);
 
-    let et = cx.sess().entry_type.get().unwrap();
+    let et = cx.sess().entry_fn.get().map(|e| e.2);
     match et {
-        config::EntryMain => create_entry_fn(cx, span, main_llfn, main_def_id, true),
-        config::EntryStart => create_entry_fn(cx, span, main_llfn, main_def_id, false),
-        config::EntryNone => {}    // Do nothing.
+        Some(config::EntryMain) => create_entry_fn(cx, span, main_llfn, main_def_id, true),
+        Some(config::EntryStart) => create_entry_fn(cx, span, main_llfn, main_def_id, false),
+        None => {}    // Do nothing.
     }
 
     fn create_entry_fn<'cx>(cx: &'cx CodegenCx,
diff --git a/src/librustc_trans/debuginfo/mod.rs b/src/librustc_trans/debuginfo/mod.rs
index 7664c88679e0..0ba11a1785ba 100644
--- a/src/librustc_trans/debuginfo/mod.rs
+++ b/src/librustc_trans/debuginfo/mod.rs
@@ -263,7 +263,7 @@ pub fn create_function_debug_context<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
 
     let local_id = cx.tcx.hir.as_local_node_id(def_id);
     match *cx.sess().entry_fn.borrow() {
-        Some((id, _)) => {
+        Some((id, _, _)) => {
             if local_id == Some(id) {
                 flags = flags | DIFlags::FlagMainSubprogram;
             }
diff --git a/src/librustc_trans_utils/lib.rs b/src/librustc_trans_utils/lib.rs
index cf47d9b62a94..a33978eeb62f 100644
--- a/src/librustc_trans_utils/lib.rs
+++ b/src/librustc_trans_utils/lib.rs
@@ -52,7 +52,7 @@ pub mod symbol_names_test;
 /// that actually test that compilation succeeds without
 /// reporting an error.
 pub fn check_for_rustc_errors_attr(tcx: TyCtxt) {
-    if let Some((id, span)) = *tcx.sess.entry_fn.borrow() {
+    if let Some((id, span, _)) = *tcx.sess.entry_fn.borrow() {
         let main_def_id = tcx.hir.local_def_id(id);
 
         if tcx.has_attr(main_def_id, "rustc_error") {
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 1308f9ef2cd0..fc60e984ea14 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -1128,10 +1128,10 @@ fn check_fn<'a, 'gcx, 'tcx>(inherited: &'a Inherited<'a, 'gcx, 'tcx>,
 
     // Check that the main return type implements the termination trait.
     if let Some(term_id) = fcx.tcx.lang_items().termination() {
-        if let Some((id, _)) = *fcx.tcx.sess.entry_fn.borrow() {
+        if let Some((id, _, entry_type)) = *fcx.tcx.sess.entry_fn.borrow() {
             if id == fn_id {
-                match fcx.sess().entry_type.get() {
-                    Some(config::EntryMain) => {
+                match entry_type {
+                    config::EntryMain => {
                         let substs = fcx.tcx.mk_substs(iter::once(Kind::from(ret_ty)));
                         let trait_ref = ty::TraitRef::new(term_id, substs);
                         let return_ty_span = decl.output.span();
@@ -1142,7 +1142,7 @@ fn check_fn<'a, 'gcx, 'tcx>(inherited: &'a Inherited<'a, 'gcx, 'tcx>,
                             traits::Obligation::new(
                                 cause, param_env, trait_ref.to_predicate()));
                     },
-                    _ => {},
+                    config::EntryStart => {},
                 }
             }
         }
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
index 6f71db998bd4..7891cc4471ff 100644
--- a/src/librustc_typeck/lib.rs
+++ b/src/librustc_typeck/lib.rs
@@ -289,12 +289,10 @@ fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 }
 
 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
-    if let Some((id, sp)) = *tcx.sess.entry_fn.borrow() {
-        match tcx.sess.entry_type.get() {
-            Some(config::EntryMain) => check_main_fn_ty(tcx, id, sp),
-            Some(config::EntryStart) => check_start_fn_ty(tcx, id, sp),
-            Some(config::EntryNone) => {}
-            None => bug!("entry function without a type")
+    if let Some((id, sp, entry_type)) = *tcx.sess.entry_fn.borrow() {
+        match entry_type {
+            config::EntryMain => check_main_fn_ty(tcx, id, sp),
+            config::EntryStart => check_start_fn_ty(tcx, id, sp),
         }
     }
 }