diff --git a/include/swift/AST/Types.h b/include/swift/AST/Types.h
index 457546af4edfd..c6b12e2e33278 100644
--- a/include/swift/AST/Types.h
+++ b/include/swift/AST/Types.h
@@ -2345,7 +2345,11 @@ class TypeAliasType final
 
   /// Retrieve the substitution map applied to the declaration's underlying
   /// to produce the described type.
-  SubstitutionMap getSubstitutionMap() const;
+  ///
+  /// \param wantContextualType If \c true, the substitution map will bind
+  /// outer local generic parameters to archetypes. Otherwise they will be left
+  /// unchanged.
+  SubstitutionMap getSubstitutionMap(bool wantContextualType = false) const;
 
   /// Get the direct generic arguments, which correspond to the generic
   /// arguments that are directly applied to the typealias declaration
diff --git a/lib/AST/Type.cpp b/lib/AST/Type.cpp
index ddbb03bb29b23..c7dbc143c2a9f 100644
--- a/lib/AST/Type.cpp
+++ b/lib/AST/Type.cpp
@@ -2155,7 +2155,8 @@ GenericSignature TypeAliasType::getGenericSignature() const {
   return typealias->getGenericSignature();
 }
 
-SubstitutionMap TypeAliasType::getSubstitutionMap() const {
+SubstitutionMap
+TypeAliasType::getSubstitutionMap(bool wantContextualType) const {
   auto genericSig = typealias->getGenericSignature();
   if (!genericSig)
     return SubstitutionMap();
@@ -2164,8 +2165,14 @@ SubstitutionMap TypeAliasType::getSubstitutionMap() const {
   DeclContext *dc = typealias->getDeclContext();
 
   if (dc->isLocalContext()) {
-    if (auto parentSig = dc->getGenericSignatureOfContext())
-      parentSubMap = parentSig->getIdentitySubstitutionMap();
+    if (auto parentSig = dc->getGenericSignatureOfContext()) {
+      if (wantContextualType) {
+        parentSubMap =
+            parentSig.getGenericEnvironment()->getForwardingSubstitutionMap();
+      } else {
+        parentSubMap = parentSig->getIdentitySubstitutionMap();
+      }
+    }
   } else if (auto parent = getParent()) {
     parentSubMap = parent->getContextSubstitutionMap(dc);
   }
diff --git a/lib/Sema/TypeOfReference.cpp b/lib/Sema/TypeOfReference.cpp
index 9f085732503e2..463ad2c16ae74 100644
--- a/lib/Sema/TypeOfReference.cpp
+++ b/lib/Sema/TypeOfReference.cpp
@@ -261,16 +261,30 @@ class InferableTypeOpener final {
   }
 
   Type transformTypeAliasType(TypeAliasType *aliasTy) {
+    auto *TAD = aliasTy->getDecl();
+
+    // For a non-generic typealias, we can simply recurse into the underlying
+    // type. The constraint system doesn't properly handle opened types in
+    // the underlying type of a typealias (e.g TypeWalker won't visit them),
+    // so we don't preserve the sugar.
+    if (!TAD->getGenericSignature())
+      return transform(aliasTy->getSinglyDesugaredType());
+
+    // Otherwise we have a generic typealias, or typealias in a generic context,
+    // and need to open any requirements introduced. Then we need to
+    // re-substitute any opened types into the underlying type. Like the
+    // non-generic codepath we also don't want to preserve sugar.
     SmallVector<Type, 4> genericArgs;
     for (auto arg : aliasTy->getDirectGenericArgs())
       genericArgs.push_back(transform(arg));
 
-    auto substTy = TypeAliasType::get(
-        aliasTy->getDecl(), transform(aliasTy->getParent()), genericArgs,
-        transform(aliasTy->getSinglyDesugaredType()));
-    openGenericTypeRequirements(substTy->getDecl(),
-                                substTy->getSubstitutionMap());
-    return substTy;
+    auto parentTy = transform(aliasTy->getParent());
+    auto subMap = TypeAliasType::get(TAD, parentTy, genericArgs,
+                                     aliasTy->getSinglyDesugaredType())
+                      ->getSubstitutionMap(/*wantContextualType*/ true);
+
+    openGenericTypeRequirements(TAD, subMap);
+    return transform(TAD->getUnderlyingType().subst(subMap));
   }
 
   Type transformErrorType(ErrorType *errTy) {
diff --git a/test/Constraints/rdar160135085.swift b/test/Constraints/rdar160135085.swift
new file mode 100644
index 0000000000000..3ac73dcff3eb9
--- /dev/null
+++ b/test/Constraints/rdar160135085.swift
@@ -0,0 +1,24 @@
+// RUN: %empty-directory(%t/modules)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend-emit-module -emit-module-path %t/modules/A.swiftmodule -module-name A %t/a.swift
+// RUN: %target-swift-frontend-emit-module -emit-module-path %t/modules/B.swiftmodule -module-name B -I %t/modules %t/b.swift
+// RUN: %target-swift-frontend -typecheck -I %t/modules %t/c.swift
+
+//--- a.swift
+
+public struct S<T> {
+  public init(_ x: T) {}
+}
+
+//--- b.swift
+
+import A
+public typealias S = A.S
+
+//--- c.swift
+
+import A
+import B
+
+_ = S(0)
diff --git a/test/Constraints/requirement_opening.swift b/test/Constraints/requirement_opening.swift
index df1900c4ba464..1fcc27e7db37a 100644
--- a/test/Constraints/requirement_opening.swift
+++ b/test/Constraints/requirement_opening.swift
@@ -1,23 +1,22 @@
 // RUN: %target-typecheck-verify-swift
 
-struct K<U> {} // expected-note 6{{'U' declared as parameter to type 'K'}}
+struct K<U> {}
 protocol Q {}
+struct ConformingType: Q {}
 
 struct S1<T: Q>: ExpressibleByArrayLiteral { // expected-note 2{{where 'T' = 'K<Int>'}}
   init(_ x: T) {}
   init(arrayLiteral: T...) {}
 }
 
-typealias R1<T: Q> = S1<T> // expected-note {{where 'T' = 'K<Int>'}} expected-note 2{{where 'T' = 'K<U>'}}
+typealias R1<T: Q> = S1<T> // expected-note 2{{where 'T' = 'K<Int>'}}
 
 func foo(_ x: K<Int>) {
   let _ = [x] as S1<K> // expected-error {{generic struct 'S1' requires that 'K<Int>' conform to 'Q'}}
   let _ = [x] as R1<K> // expected-error {{generic type alias 'R1' requires that 'K<Int>' conform to 'Q'}}
 
-  let _: S1<K> = [x]   // expected-error {{generic struct 'S1' requires that 'K<Int>' conform to 'Q'}}
-  // FIXME: We ought to be able to infer 'U' here.
-  let _: R1<K> = [x] // expected-error 2 {{generic type alias 'R1' requires that 'K<U>' conform to 'Q'}}
-  // expected-error@-1 2 {{generic parameter 'U' could not be inferred}}
+  let _: S1<K> = [x] // expected-error {{generic struct 'S1' requires that 'K<Int>' conform to 'Q'}}
+  let _: R1<K> = [x] // expected-error {{generic type alias 'R1' requires that 'K<Int>' conform to 'Q'}}
 }
 
 protocol P2 {
@@ -25,11 +24,11 @@ protocol P2 {
 }
 
 struct S2<A: Q>: P2 {} // expected-note 3{{where 'A' = 'K<Int>'}}
-typealias R2<A: Q> = S2<A> // expected-note 2{{where 'A' = 'K<Int>'}} expected-note 2{{where 'A' = 'K<U>'}}
+typealias R2<A: Q> = S2<A> // expected-note 3{{where 'A' = 'K<Int>'}}
 
 // Same as S2, but without the Q requirement.
 struct S3<A>: P2 {}
-typealias R3<A: Q> = S3<A> // expected-note {{where 'A' = 'K<Int>'}} expected-note {{where 'A' = 'K<U>'}}
+typealias R3<A: Q> = S3<A> // expected-note 2{{where 'A' = 'K<Int>'}}
 
 func foo<T: P2>(_ y: T.A.Type) -> T {}
 let _ = foo(K<Int>.self) as S2<K> // expected-error {{generic struct 'S2' requires that 'K<Int>' conform to 'Q'}}
@@ -37,11 +36,8 @@ let _ = foo(K<Int>.self) as R2<K> // expected-error {{generic type alias 'R2' re
 let _ = foo(K<Int>.self) as R3<K> // expected-error {{generic type alias 'R3' requires that 'K<Int>' conform to 'Q'}}
 
 let _: S2<K> = foo(K<Int>.self)   // expected-error {{generic struct 'S2' requires that 'K<Int>' conform to 'Q'}}
-// FIXME: We ought to be able to infer 'U' here.
-let _: R2<K> = foo(K<Int>.self)   // expected-error 2{{generic type alias 'R2' requires that 'K<U>' conform to 'Q'}}
-// expected-error@-1 2 {{generic parameter 'U' could not be inferred}}
-let _: R3<K> = foo(K<Int>.self)   // expected-error {{generic type alias 'R3' requires that 'K<U>' conform to 'Q'}}
-// expected-error@-1 2 {{generic parameter 'U' could not be inferred}}
+let _: R2<K> = foo(K<Int>.self)   // expected-error {{generic type alias 'R2' requires that 'K<Int>' conform to 'Q'}}
+let _: R3<K> = foo(K<Int>.self)   // expected-error {{generic type alias 'R3' requires that 'K<Int>' conform to 'Q'}}
 
 func foo<T: P2>(_ x: T.Type, _ y: T.A.Type) {}
 foo(S2<_>.self, K<Int>.self) // expected-error {{generic struct 'S2' requires that 'K<Int>' conform to 'Q'}}
@@ -52,3 +48,17 @@ struct S4<T: Q> { // expected-note {{where 'T' = 'Int'}}
 }
 
 _ = S4<_>(0) // expected-error {{generic struct 'S4' requires that 'Int' conform to 'Q'}}
+
+func testLocalOuterGeneric<T>(_ x: T) {
+  typealias X<U: Q> = (T, U) // expected-note {{where 'U' = 'String'}}
+  let _: X<_> = (x, "") // expected-error {{generic type alias 'X' requires that 'String' conform to 'Q'}}
+  let _: X<_> = (x, ConformingType())
+}
+
+struct TestParentGeneric<T> {
+  typealias X<U: Q> = (T, U) // expected-note {{where 'U' = 'String'}}
+  func bar(_ x: T) {
+    let _: X<_> = (x, "") // expected-error {{generic type alias 'X' requires that 'String' conform to 'Q'}}
+    let _: X<_> = (x, ConformingType())
+  }
+}
diff --git a/test/decl/typealias/generic.swift b/test/decl/typealias/generic.swift
index 75a893ba3d099..46995b8896481 100644
--- a/test/decl/typealias/generic.swift
+++ b/test/decl/typealias/generic.swift
@@ -465,3 +465,19 @@ func testSugar(_ gx: GX<Int>, _ gy: GX<Int>.GY<Double>, gz: GX<Int>.GY<Double>.E
   let i2: Int = gy  // expected-error{{cannot convert value of type 'GX<Int>.GY<Double>' (aka 'Array<Double>') to specified type 'Int'}}
   let i3: Int = gz // expected-error{{cannot convert value of type 'GX<Int>.GY<Double>.Element' (aka 'Double') to specified type 'Int'}}
 }
+
+func testLocalRequirementInference<T>(_ x: T, y: Int, s: S) {
+  typealias X<U: P> = (T, U) where T == U.A
+  func foo<V>(_ x: X<V>) {} // expected-note {{where 'V' = 'Int'}} expected-note {{where 'T' = 'T', 'V.A' = 'S.A' (aka 'Float')}}
+  foo((x, y)) // expected-error {{local function 'foo' requires that 'Int' conform to 'P'}}
+  foo((x, s)) // expected-error {{local function 'foo' requires the types 'T' and 'S.A' (aka 'Float') be equivalent}}
+}
+
+struct TestNestedRequirementInference<T> {
+  typealias X<U: P> = (T, U) where T == U.A
+  func foo<V>(_ x: X<V>) {} // expected-note {{where 'V' = 'Int'}} expected-note {{where 'T' = 'T', 'V.A' = 'S.A' (aka 'Float')}}
+  func bar(_ x: T, y: Int, s: S) {
+    foo((x, y)) // expected-error {{instance method 'foo' requires that 'Int' conform to 'P'}}
+    foo((x, s)) // expected-error {{instance method 'foo' requires the types 'T' and 'S.A' (aka 'Float') be equivalent}}
+  }
+}
diff --git a/validation-test/compiler_crashers_2_fixed/078aab8ab466b66a.swift b/validation-test/compiler_crashers_2_fixed/078aab8ab466b66a.swift
new file mode 100644
index 0000000000000..315bb7d79a3af
--- /dev/null
+++ b/validation-test/compiler_crashers_2_fixed/078aab8ab466b66a.swift
@@ -0,0 +1,6 @@
+// {"kind":"typecheck","signature":"swift::constraints::ConstraintSystem::openGenericParameters(swift::DeclContext*, swift::GenericSignature, llvm::SmallVectorImpl<std::__1::pair<swift::GenericTypeParamType*, swift::TypeVariableType*>>&, swift::constraints::ConstraintLocatorBuilder, swift::constraints::PreparedOverloadBuilder*)","signatureAssert":"Assertion failed: (sig), function openGenericParameters"}
+// RUN: not %target-swift-frontend -typecheck %s
+class a<b
+  func c -> d
+  typealias c  :  a
+c
diff --git a/validation-test/compiler_crashers_2_fixed/b31917ad9b8e4fe4.swift b/validation-test/compiler_crashers_2_fixed/b31917ad9b8e4fe4.swift
new file mode 100644
index 0000000000000..bc8b7f7579bd1
--- /dev/null
+++ b/validation-test/compiler_crashers_2_fixed/b31917ad9b8e4fe4.swift
@@ -0,0 +1,8 @@
+// {"kind":"typecheck","original":"0df5dc82","signature":"swift::constraints::ConstraintSystem::typeVarOccursInType(swift::TypeVariableType*, swift::Type, bool*)","signatureAssert":"Assertion failed: ((!typeVariables.empty() || hasError()) && \"Did not find type variables!\"), function getTypeVariables"}
+// RUN: not %target-swift-frontend -typecheck %s
+struct a<each b {
+  typealias d<c> = (
+  >  func  1 {
+    typealias e = f
+    e
+    typealias e = d