diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index b8b00302440..1ec7702af79 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -448,7 +448,7 @@ impl<'tcx> EntryKind<'tcx> {
             EntryKind::Mod(_) => DefKind::Mod,
             EntryKind::Variant(_) => DefKind::Variant,
             EntryKind::Trait(_) => DefKind::Trait,
-            EntryKind::TraitAlias(_) => DefKind::TraitAlias,
+            EntryKind::TraitAlias => DefKind::TraitAlias,
             EntryKind::Enum(..) => DefKind::Enum,
             EntryKind::MacroDef(_) => DefKind::Macro(MacroKind::Bang),
             EntryKind::ForeignType => DefKind::ForeignTy,
@@ -575,7 +575,7 @@ impl<'a, 'tcx> CrateMetadata {
                                   data.is_marker,
                                   self.def_path_table.def_path_hash(item_id))
             },
-            EntryKind::TraitAlias(_) => {
+            EntryKind::TraitAlias => {
                 ty::TraitDef::new(self.local_def_id(item_id),
                                   hir::Unsafety::Normal,
                                   false,
@@ -680,13 +680,7 @@ impl<'a, 'tcx> CrateMetadata {
         item_id: DefIndex,
         tcx: TyCtxt<'tcx>,
     ) -> ty::GenericPredicates<'tcx> {
-        let super_predicates = match self.kind(item_id) {
-            EntryKind::Trait(data) => data.decode(self).super_predicates,
-            EntryKind::TraitAlias(data) => data.decode(self).super_predicates,
-            _ => bug!("def-index does not refer to trait or trait alias"),
-        };
-
-        super_predicates.decode((self, tcx))
+        self.root.per_def.super_predicates.get(self, item_id).unwrap().decode((self, tcx))
     }
 
     crate fn get_generics(&self, item_id: DefIndex, sess: &Session) -> ty::Generics {
@@ -1118,7 +1112,7 @@ impl<'a, 'tcx> CrateMetadata {
         def_key.parent.and_then(|parent_index| {
             match self.kind(parent_index) {
                 EntryKind::Trait(_) |
-                EntryKind::TraitAlias(_) => Some(self.local_def_id(parent_index)),
+                EntryKind::TraitAlias => Some(self.local_def_id(parent_index)),
                 _ => None,
             }
         })
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index 6ae8c2fc6c6..79a7caa292b 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -76,6 +76,7 @@ struct PerDefTables<'tcx> {
     generics: PerDefTable<Lazy<ty::Generics>>,
     predicates: PerDefTable<Lazy<ty::GenericPredicates<'tcx>>>,
     predicates_defined_on: PerDefTable<Lazy<ty::GenericPredicates<'tcx>>>,
+    super_predicates: PerDefTable<Lazy<ty::GenericPredicates<'tcx>>>,
 
     mir: PerDefTable<Lazy<mir::Body<'tcx>>>,
     promoted_mir: PerDefTable<Lazy<IndexVec<mir::Promoted, mir::Body<'tcx>>>>,
@@ -513,6 +514,7 @@ impl<'tcx> EncodeContext<'tcx> {
             generics: self.per_def.generics.encode(&mut self.opaque),
             predicates: self.per_def.predicates.encode(&mut self.opaque),
             predicates_defined_on: self.per_def.predicates_defined_on.encode(&mut self.opaque),
+            super_predicates: self.per_def.super_predicates.encode(&mut self.opaque),
 
             mir: self.per_def.mir.encode(&mut self.opaque),
             promoted_mir: self.per_def.promoted_mir.encode(&mut self.opaque),
@@ -835,6 +837,11 @@ impl EncodeContext<'tcx> {
             self.tcx.predicates_defined_on(def_id))
     }
 
+    fn encode_super_predicates(&mut self, def_id: DefId) {
+        debug!("EncodeContext::encode_super_predicates({:?})", def_id);
+        record!(self.per_def.super_predicates[def_id] <- self.tcx.super_predicates_of(def_id));
+    }
+
     fn encode_info_for_trait_item(&mut self, def_id: DefId) {
         debug!("EncodeContext::encode_info_for_trait_item({:?})", def_id);
         let tcx = self.tcx;
@@ -1166,18 +1173,11 @@ impl EncodeContext<'tcx> {
                     paren_sugar: trait_def.paren_sugar,
                     has_auto_impl: self.tcx.trait_is_auto(def_id),
                     is_marker: trait_def.is_marker,
-                    super_predicates: self.lazy(tcx.super_predicates_of(def_id)),
                 };
 
                 EntryKind::Trait(self.lazy(data))
             }
-            hir::ItemKind::TraitAlias(..) => {
-                let data = TraitAliasData {
-                    super_predicates: self.lazy(tcx.super_predicates_of(def_id)),
-                };
-
-                EntryKind::TraitAlias(self.lazy(data))
-            }
+            hir::ItemKind::TraitAlias(..) => EntryKind::TraitAlias,
             hir::ItemKind::ExternCrate(_) |
             hir::ItemKind::Use(..) => bug!("cannot encode info for item {:?}", item),
         });
@@ -1269,6 +1269,13 @@ impl EncodeContext<'tcx> {
             }
             _ => {} // not *wrong* for other kinds of items, but not needed
         }
+        match item.kind {
+            hir::ItemKind::Trait(..) |
+            hir::ItemKind::TraitAlias(..) => {
+                self.encode_super_predicates(def_id);
+            }
+            _ => {}
+        }
 
         let mir = match item.kind {
             hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => true,
diff --git a/src/librustc_metadata/schema.rs b/src/librustc_metadata/schema.rs
index 96f35783278..b681078ee0d 100644
--- a/src/librustc_metadata/schema.rs
+++ b/src/librustc_metadata/schema.rs
@@ -243,6 +243,7 @@ crate struct LazyPerDefTables<'tcx> {
     pub generics: Lazy!(PerDefTable<Lazy<ty::Generics>>),
     pub predicates: Lazy!(PerDefTable<Lazy!(ty::GenericPredicates<'tcx>)>),
     pub predicates_defined_on: Lazy!(PerDefTable<Lazy!(ty::GenericPredicates<'tcx>)>),
+    pub super_predicates: Lazy!(PerDefTable<Lazy!(ty::GenericPredicates<'tcx>)>),
 
     pub mir: Lazy!(PerDefTable<Lazy!(mir::Body<'tcx>)>),
     pub promoted_mir: Lazy!(PerDefTable<Lazy!(IndexVec<mir::Promoted, mir::Body<'tcx>>)>),
@@ -273,13 +274,13 @@ crate enum EntryKind<'tcx> {
     MacroDef(Lazy<MacroDef>),
     Closure(Lazy!(ClosureData<'tcx>)),
     Generator(Lazy!(GeneratorData<'tcx>)),
-    Trait(Lazy!(TraitData<'tcx>)),
+    Trait(Lazy<TraitData>),
     Impl(Lazy!(ImplData<'tcx>)),
     Method(Lazy!(MethodData<'tcx>)),
     AssocType(AssocContainer),
     AssocOpaqueTy(AssocContainer),
     AssocConst(AssocContainer, ConstQualif, Lazy<RenderedConst>),
-    TraitAlias(Lazy!(TraitAliasData<'tcx>)),
+    TraitAlias,
 }
 
 /// Additional data for EntryKind::Const and EntryKind::AssocConst
@@ -324,17 +325,11 @@ crate struct VariantData<'tcx> {
 }
 
 #[derive(RustcEncodable, RustcDecodable)]
-crate struct TraitData<'tcx> {
+crate struct TraitData {
     pub unsafety: hir::Unsafety,
     pub paren_sugar: bool,
     pub has_auto_impl: bool,
     pub is_marker: bool,
-    pub super_predicates: Lazy!(ty::GenericPredicates<'tcx>),
-}
-
-#[derive(RustcEncodable, RustcDecodable)]
-crate struct TraitAliasData<'tcx> {
-    pub super_predicates: Lazy!(ty::GenericPredicates<'tcx>),
 }
 
 #[derive(RustcEncodable, RustcDecodable)]