diff --git a/chalk-parse/src/ast.rs b/chalk-parse/src/ast.rs
index a63f708da6d..5affaaae3e0 100644
--- a/chalk-parse/src/ast.rs
+++ b/chalk-parse/src/ast.rs
@@ -54,6 +54,8 @@ pub struct TraitFlags {
 pub struct AssocTyDefn {
     pub name: Identifier,
     pub parameter_kinds: Vec<ParameterKind>,
+    pub bounds: Vec<InlineBound>,
+    pub where_clauses: Vec<QuantifiedWhereClause>,
 }
 
 pub enum ParameterKind {
@@ -66,6 +68,28 @@ pub enum Parameter {
     Lifetime(Lifetime),
 }
 
+/// An inline bound, e.g. `: Foo<K>` in `impl<K, T: Foo<K>> SomeType<T>`.
+pub enum InlineBound {
+    TraitBound(TraitBound),
+    ProjectionEqBound(ProjectionEqBound),
+}
+
+/// Represents a trait bound on e.g. a type or type parameter.
+/// Does not know anything about what it's binding.
+pub struct TraitBound {
+    pub trait_name: Identifier,
+    pub args_no_self: Vec<Parameter>,
+}
+
+/// Represents a projection equality bound on e.g. a type or type parameter.
+/// Does not know anything about what it's binding.
+pub struct ProjectionEqBound {
+    pub trait_bound: TraitBound,
+    pub name: Identifier,
+    pub parameters: Vec<Parameter>,
+    pub value: Ty,
+}
+
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum Kind {
     Ty,
@@ -115,7 +139,6 @@ pub struct Impl {
 pub struct AssocTyValue {
     pub name: Identifier,
     pub parameter_kinds: Vec<ParameterKind>,
-    pub where_clauses: Vec<WhereClause>,
     pub value: Ty,
 }
 
diff --git a/chalk-parse/src/parser.lalrpop b/chalk-parse/src/parser.lalrpop
index 71b528092ae..a043f68eb3d 100644
--- a/chalk-parse/src/parser.lalrpop
+++ b/chalk-parse/src/parser.lalrpop
@@ -72,9 +72,43 @@ TraitDefn: TraitDefn = {
 };
 
 AssocTyDefn: AssocTyDefn = {
-    "type" <name:Id> <p:Angle<ParameterKind>> ";" => AssocTyDefn {
-        name: name,
-        parameter_kinds: p
+    "type" <name:Id> <p:Angle<ParameterKind>> <b:(":" <Plus<InlineBound>>)?>
+        <w:QuantifiedWhereClauses> ";" =>
+    {
+        AssocTyDefn {
+            name: name,
+            parameter_kinds: p,
+            where_clauses: w,
+            bounds: b.unwrap_or(vec![]),
+        }
+    }
+};
+
+InlineBound: InlineBound = {
+    TraitBound => InlineBound::TraitBound(<>),
+    ProjectionEqBound => InlineBound::ProjectionEqBound(<>),
+};
+
+TraitBound: TraitBound = {
+    <t:Id> <a:Angle<Parameter>> => {
+        TraitBound {
+            trait_name: t,
+            args_no_self: a,
+        }
+    }
+};
+
+ProjectionEqBound: ProjectionEqBound = {
+    <t:Id> "<" <a:(<Comma<Parameter>> ",")?> <name:Id> <a2:Angle<Parameter>>
+        "=" <ty:Ty> ">" => ProjectionEqBound
+    {
+        trait_bound: TraitBound {
+            trait_name: t,
+            args_no_self: a.unwrap_or(vec![]),
+        },
+        name,
+        parameters: a2,
+        value: ty,
     }
 };
 
@@ -102,11 +136,10 @@ ParameterKind: ParameterKind = {
 };
 
 AssocTyValue: AssocTyValue = {
-    "type" <n:Id> <a:Angle<ParameterKind>> <wc:WhereClauses> "=" <v:Ty> ";" => AssocTyValue {
+    "type" <n:Id> <a:Angle<ParameterKind>> "=" <v:Ty> ";" => AssocTyValue {
         name: n,
         parameter_kinds: a,
         value: v,
-        where_clauses: wc,
     },
 };
 
@@ -201,11 +234,6 @@ InlineClause: Clause = {
     }
 };
 
-WhereClauses: Vec<WhereClause> = {
-    "where" <Comma<WhereClause>>,
-    () => vec![],
-};
-
 QuantifiedWhereClauses: Vec<QuantifiedWhereClause> = {
     "where" <Comma<QuantifiedWhereClause>>,
     () => vec![],
@@ -290,6 +318,11 @@ SemiColon<T>: Vec<T> = {
     <Separator<";", T>>
 };
 
+#[inline]
+Plus<T>: Vec<T> = {
+    <Separator<"+", T>>
+};
+
 Angle<T>: Vec<T> = {
     "<" <Comma<T>> ">",
     () => vec![],
diff --git a/src/fold/mod.rs b/src/fold/mod.rs
index d121d36a1f3..1fa900e7041 100644
--- a/src/fold/mod.rs
+++ b/src/fold/mod.rs
@@ -567,7 +567,7 @@ struct_fold!(AssociatedTyValue {
     associated_ty_id,
     value,
 });
-struct_fold!(AssociatedTyValueBound { ty, where_clauses });
+struct_fold!(AssociatedTyValueBound { ty });
 struct_fold!(Environment { clauses });
 struct_fold!(InEnvironment[F] { environment, goal } where F: Fold<Result = F>);
 struct_fold!(EqGoal { a, b });
diff --git a/src/ir/lowering/mod.rs b/src/ir/lowering/mod.rs
index 395c8cca4ba..34d51cbd592 100644
--- a/src/ir/lowering/mod.rs
+++ b/src/ir/lowering/mod.rs
@@ -70,7 +70,7 @@ impl<'k> Env<'k> {
     /// Introduces new parameters, shifting the indices of existing
     /// parameters to accommodate them. The indices of the new binders
     /// will be assigned in order as they are iterated.
-    fn introduce<I>(&self, binders: I) -> Self
+    fn introduce<I>(&self, binders: I) -> Result<Self>
     where
         I: IntoIterator<Item = ir::ParameterKind<ir::Identifier>>,
         I::IntoIter: ExactSizeIterator,
@@ -82,10 +82,13 @@ impl<'k> Env<'k> {
             .map(|(&k, &v)| (k, v + len))
             .chain(binders)
             .collect();
-        Env {
+        if parameter_map.len() != self.parameter_map.len() + len {
+            bail!("duplicate parameters");
+        }
+        Ok(Env {
             parameter_map,
             ..*self
-        }
+        })
     }
 
     fn in_binders<I, T, OP>(&self, binders: I, op: OP) -> Result<ir::Binders<T>>
@@ -95,7 +98,7 @@ impl<'k> Env<'k> {
         OP: FnOnce(&Self) -> Result<T>,
     {
         let binders: Vec<_> = binders.into_iter().collect();
-        let env = self.introduce(binders.iter().cloned());
+        let env = self.introduce(binders.iter().cloned())?;
         Ok(ir::Binders {
             binders: binders.anonymize(),
             value: op(&env)?,
@@ -178,6 +181,7 @@ impl LowerProgram for Program {
 
                         let mut parameter_kinds = defn.all_parameters();
                         parameter_kinds.extend(d.all_parameters());
+                        let env = empty_env.introduce(parameter_kinds.clone())?;
 
                         associated_ty_data.insert(
                             info.id,
@@ -186,7 +190,7 @@ impl LowerProgram for Program {
                                 id: info.id,
                                 name: defn.name.str,
                                 parameter_kinds: parameter_kinds,
-                                where_clauses: vec![],
+                                where_clauses: defn.where_clauses.lower(&env)?,
                             },
                         );
                     }
@@ -757,7 +761,7 @@ impl LowerTy for Ty {
                     lifetime_names
                         .iter()
                         .map(|id| ir::ParameterKind::Lifetime(id.str)),
-                );
+                )?;
 
                 let ty = ty.lower(&quantified_env)?;
                 let quantified_ty = ir::QuantifiedTy {
@@ -872,7 +876,6 @@ impl LowerAssocTyValue for AssocTyValue {
         let value = env.in_binders(self.all_parameters(), |env| {
             Ok(ir::AssociatedTyValueBound {
                 ty: self.value.lower(env)?,
-                where_clauses: self.where_clauses.lower(env)?,
             })
         })?;
         Ok(ir::AssociatedTyValue {
diff --git a/src/ir/lowering/test.rs b/src/ir/lowering/test.rs
index e23413f10aa..f97a10e27bd 100644
--- a/src/ir/lowering/test.rs
+++ b/src/ir/lowering/test.rs
@@ -211,8 +211,7 @@ fn atc_accounting() {
             AssociatedTyValue {
                 associated_ty_id: (Iterable::Iter),
                 value: for<lifetime> AssociatedTyValueBound {
-                    ty: Iter<'?0, ?1>,
-                    where_clauses: []
+                    ty: Iter<'?0, ?1>
                 }
             }
         ],
@@ -303,3 +302,71 @@ fn check_parameter_kinds() {
         }
     }
 }
+
+#[test]
+fn gat_parse() {
+    lowering_success! {
+        program {
+            trait Sized {}
+
+            trait Foo {
+                type Item<'a, T>: Sized + Clone where Self: Sized;
+            }
+
+            trait Bar {
+                type Item<'a, T> where Self: Sized;
+            }
+
+            struct Container<T> {
+                value: T
+            }
+
+            trait Baz {
+                type Item<'a, 'b, T>: Foo<Item<'b, T> = Container<T>> + Clone;
+            }
+
+            trait Quux {
+                type Item<'a, T>;
+            }
+        }
+    }
+
+    lowering_error! {
+        program {
+            trait Sized { }
+
+            trait Foo {
+                type Item where K: Sized;
+            }
+        }
+
+        error_msg {
+            "invalid type name `K`"
+        }
+    }
+}
+
+#[test]
+fn duplicate_parameters() {
+    lowering_error! {
+        program {
+            trait Foo<T, T> { }
+        }
+
+        error_msg {
+            "duplicate parameters"
+        }
+    }
+
+    lowering_error! {
+        program {
+            trait Foo<T> {
+                type Item<T>;
+            }
+        }
+
+        error_msg {
+            "duplicate parameters"
+        }
+    }
+}
diff --git a/src/ir/mod.rs b/src/ir/mod.rs
index 66844c61b9f..e99392f71f4 100644
--- a/src/ir/mod.rs
+++ b/src/ir/mod.rs
@@ -273,8 +273,10 @@ pub struct AssociatedTyDatum {
     /// but possibly including more.
     crate parameter_kinds: Vec<ParameterKind<Identifier>>,
 
+    // FIXME: inline bounds on the associated ty need to be implemented
+
     /// Where clauses that must hold for the projection be well-formed.
-    crate where_clauses: Vec<DomainGoal>,
+    crate where_clauses: Vec<QuantifiedDomainGoal>,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -289,10 +291,6 @@ pub struct AssociatedTyValue {
 pub struct AssociatedTyValueBound {
     /// Type that we normalize to. The X in `type Foo<'a> = X`.
     crate ty: Ty,
-
-    /// Where-clauses that must hold for projection to be valid. The
-    /// WC in `type Foo<'a> = X where WC`.
-    crate where_clauses: Vec<DomainGoal>,
 }
 
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
diff --git a/src/lib.rs b/src/lib.rs
index c8dbaf5e029..e20ec4a7849 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,13 +3,11 @@
 #![feature(catch_expr)]
 #![feature(crate_in_paths)]
 #![feature(crate_visibility_modifier)]
-#![feature(dyn_trait)]
 #![feature(in_band_lifetimes)]
 #![feature(macro_at_most_once_rep)]
 #![feature(macro_vis_matcher)]
 #![feature(specialization)]
 #![feature(step_trait)]
-#![feature(underscore_lifetimes)]
 
 extern crate chalk_parse;
 #[macro_use]
diff --git a/src/rules/mod.rs b/src/rules/mod.rs
index 2ced3cc2f8c..522a52132ef 100644
--- a/src/rules/mod.rs
+++ b/src/rules/mod.rs
@@ -200,10 +200,7 @@ impl ir::AssociatedTyValue {
             .trait_ref
             .trait_ref()
             .up_shift(self.value.len());
-        let conditions: Vec<ir::Goal> = Some(impl_trait_ref.clone().cast())
-            .into_iter()
-            .chain(self.value.value.where_clauses.clone().cast())
-            .collect();
+        let conditions: Vec<ir::Goal> = vec![impl_trait_ref.clone().cast()];
 
         // Bound parameters + `Self` type of the trait-ref
         let parameters: Vec<_> = {