diff --git a/crates/ra_hir/src/generics.rs b/crates/ra_hir/src/generics.rs
index e6482180d5c..e75337cdf75 100644
--- a/crates/ra_hir/src/generics.rs
+++ b/crates/ra_hir/src/generics.rs
@@ -75,6 +75,7 @@ impl GenericParams {
         };
         generics.parent_params = parent.map(|p| db.generic_params(p));
         let start = generics.parent_params.as_ref().map(|p| p.params.len()).unwrap_or(0) as u32;
+        // FIXME: add `: Sized` bound for everything except for `Self` in traits
         match def {
             GenericDef::Function(it) => generics.fill(&it.source(db).ast, start),
             GenericDef::Struct(it) => generics.fill(&it.source(db).ast, start),
@@ -86,6 +87,9 @@ impl GenericParams {
                 generics.fill(&it.source(db).ast, start + 1);
             }
             GenericDef::TypeAlias(it) => generics.fill(&it.source(db).ast, start),
+            // Note that we don't add `Self` here: in `impl`s, `Self` is not a
+            // type-parameter, but rather is a type-alias for impl's target
+            // type, so this is handled by the resovler.
             GenericDef::ImplBlock(it) => generics.fill(&it.source(db).ast, start),
             GenericDef::EnumVariant(_) => {}
         }
@@ -135,6 +139,10 @@ impl GenericParams {
     }
 
     fn add_where_predicate_from_bound(&mut self, bound: ast::TypeBound, type_ref: TypeRef) {
+        if bound.has_question_mark() {
+            // FIXME: remove this bound
+            return;
+        }
         let path = bound
             .type_ref()
             .and_then(|tr| match tr {
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 6c2d857bca1..57fd5492d8b 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -3028,6 +3028,35 @@ fn test(s: S) {
     assert_eq!(t, "{unknown}");
 }
 
+#[test]
+fn deref_trait_with_question_mark_size() {
+    let t = type_at(
+        r#"
+//- /main.rs
+#[lang = "deref"]
+trait Deref {
+    type Target;
+    fn deref(&self) -> &Self::Target;
+}
+
+struct Arc<T>;
+impl<T: ?Sized> Deref for Arc<T> {
+    type Target = T;
+}
+
+struct S;
+impl S {
+    fn foo(&self) -> u128 {}
+}
+
+fn test(s: Arc<S>) {
+    (*s, s.foo())<|>
+}
+"#,
+    );
+    assert_eq!(t, "(S, u128)");
+}
+
 #[test]
 fn obligation_from_function_clause() {
     let t = type_at(
diff --git a/crates/ra_syntax/src/ast/extensions.rs b/crates/ra_syntax/src/ast/extensions.rs
index 2a59cf65373..efe261fc232 100644
--- a/crates/ra_syntax/src/ast/extensions.rs
+++ b/crates/ra_syntax/src/ast/extensions.rs
@@ -382,6 +382,18 @@ impl ast::WherePred {
     }
 }
 
+impl ast::TypeBound {
+    pub fn question_mark_token(&self) -> Option<SyntaxToken> {
+        self.syntax()
+            .children_with_tokens()
+            .filter_map(|it| it.into_token())
+            .find(|it| it.kind() == T![?])
+    }
+    pub fn has_question_mark(&self) -> bool {
+        self.question_mark_token().is_some()
+    }
+}
+
 impl ast::TraitDef {
     pub fn is_auto(&self) -> bool {
         self.syntax().children_with_tokens().any(|t| t.kind() == T![auto])