diff --git a/lib/Sema/CSRanking.cpp b/lib/Sema/CSRanking.cpp
index 9830c66dbe91e..58bfe17faa44d 100644
--- a/lib/Sema/CSRanking.cpp
+++ b/lib/Sema/CSRanking.cpp
@@ -195,16 +195,28 @@ static bool sameDecl(Decl *decl1, Decl *decl2) {
   if (decl1 == decl2)
     return true;
 
-  // All types considered identical.
-  // FIXME: This is a hack. What we really want is to have substituted the
-  // base type into the declaration reference, so that we can compare the
-  // actual types to which two type declarations resolve. If those types are
-  // equivalent, then it doesn't matter which declaration is chosen.
-  if (isa<TypeDecl>(decl1) && isa<TypeDecl>(decl2))
-    return true;
-  
-  if (decl1->getKind() != decl2->getKind())
-    return false;
+  // Special hack to allow type aliases with same underlying type.
+  //
+  // FIXME: Check substituted types instead.
+  //
+  // FIXME: Perhaps this should be handled earlier in name lookup.
+  auto *typeDecl1 = dyn_cast<TypeDecl>(decl1);
+  auto *typeDecl2 = dyn_cast<TypeDecl>(decl2);
+  if (typeDecl1 && typeDecl2) {
+    auto type1 = typeDecl1->getDeclaredInterfaceType();
+    auto type2 = typeDecl2->getDeclaredInterfaceType();
+
+    // Handle unbound generic type aliases, eg
+    //
+    // struct Array<Element> {}
+    // typealias MyArray = Array
+    if (type1->is<UnboundGenericType>())
+      type1 = type1->getAnyNominal()->getDeclaredInterfaceType();
+    if (type2->is<UnboundGenericType>())
+      type2 = type2->getAnyNominal()->getDeclaredInterfaceType();
+
+    return type1->isEqual(type2);
+  }
 
   return false;
 }
diff --git a/test/AssociatedTypeInference/type_witness_from_parameterized_protocol.swift b/test/AssociatedTypeInference/type_witness_from_parameterized_protocol.swift
index 81aff5087217a..aef02ec1946f6 100644
--- a/test/AssociatedTypeInference/type_witness_from_parameterized_protocol.swift
+++ b/test/AssociatedTypeInference/type_witness_from_parameterized_protocol.swift
@@ -43,10 +43,12 @@ struct S4: (P & Q<String>) & R {
 }
 
 struct Bad: P<Int, Float> { // expected-error {{type 'Bad' does not conform to protocol 'P'}}
-  typealias A = String  // expected-note {{possibly intended match}}
+  typealias A = String
+  // expected-note@-1 {{possibly intended match}}
+  // expected-note@-2 {{found this candidate}}
 }
 
-let x = Bad.A.self
+let x = Bad.A.self // expected-error {{ambiguous use of 'A'}}
 g(x)
 
 struct Circle: Q<Circle.A> {}
diff --git a/test/Constraints/ambiguous_specialized_name_diagnostics.swift b/test/Constraints/ambiguous_specialized_name_diagnostics.swift
index 3ecf7d8d6cfe9..84107a18ec25d 100644
--- a/test/Constraints/ambiguous_specialized_name_diagnostics.swift
+++ b/test/Constraints/ambiguous_specialized_name_diagnostics.swift
@@ -38,10 +38,10 @@ import A
 import B
 
 func test() {
-  _ = S<Int>(t: 42) // expected-error {{ambiguous use of 'init(t:)'}}
+  _ = S<Int>(t: 42) // expected-error {{ambiguous use of 'S'}}
 
-  S<Int>(t: 42).test() // expected-error {{ambiguous use of 'init(t:)'}}
+  S<Int>(t: 42).test() // expected-error {{ambiguous use of 'S'}}
 
   S<Int>.staticFn()
-  // expected-error@-1 {{ambiguous use of 'staticFn()'}}
+  // expected-error@-1 {{ambiguous use of 'S'}}
 }
diff --git a/test/Constraints/invalid_decl_ref.swift b/test/Constraints/invalid_decl_ref.swift
index 7c65fa085435a..ca80822bc6e69 100644
--- a/test/Constraints/invalid_decl_ref.swift
+++ b/test/Constraints/invalid_decl_ref.swift
@@ -1,9 +1,7 @@
-// RUN: %target-swift-frontend -module-name SomeModule -typecheck -verify -dump-ast -import-objc-header %S/Inputs/imported_type.h %s | %FileCheck %s
+// RUN: %target-swift-frontend -module-name SomeModule -typecheck -verify -import-objc-header %S/Inputs/imported_type.h %s -verify-ignore-unrelated
 
 // REQUIRES: objc_interop
 
 import Foundation
 
-// CHECK: declref_expr type="module<SomeModule>"
-// CHECK-NEXT: type_expr type="Data.Type"
-let type = SomeModule.Data.self
+let type = SomeModule.Data.self // expected-error {{ambiguous use of 'Data'}}
diff --git a/test/Constraints/rdar165863775.swift b/test/Constraints/rdar165863775.swift
new file mode 100644
index 0000000000000..46770eecf2e98
--- /dev/null
+++ b/test/Constraints/rdar165863775.swift
@@ -0,0 +1,40 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+// RUN: %target-swift-frontend -emit-module %t/src/A.swift \
+// RUN:   -module-name A \
+// RUN:   -emit-module-path %t/A.swiftmodule
+
+// RUN: %target-swift-frontend -emit-module %t/src/B.swift \
+// RUN:   -module-name B \
+// RUN:   -emit-module-path %t/B.swiftmodule
+
+// RUN: %target-swift-frontend -typecheck -verify -verify-ignore-unrelated -module-name main -I %t %t/src/main.swift
+
+//--- A.swift
+public struct Bag {
+}
+
+//--- B.swift
+public struct Bag {
+}
+
+//--- main.swift
+import A
+import B
+
+protocol P {
+}
+
+struct Test {
+    func inject<T>(_: T.Type = T.self) {}
+
+    func inject<T: P>(_: T) {}
+
+    func inject<T>(_: T) async -> T {}
+}
+
+func test(t: Test) {
+    t.inject(Bag.self)  // expected-error {{ambiguous use of 'Bag'}}
+}
diff --git a/test/NameLookup/member_import_visibility.swift b/test/NameLookup/member_import_visibility.swift
index 741dadc37b27c..6b664630aba87 100644
--- a/test/NameLookup/member_import_visibility.swift
+++ b/test/NameLookup/member_import_visibility.swift
@@ -85,7 +85,7 @@ extension X {
     _ = (NestedInA, NestedInB, NestedInC).self // expected-member-visibility-error{{struct 'NestedInB' is not available due to missing import of defining module 'members_B'}}
     _ = GenericType<NestedInB>.self // expected-member-visibility-error{{struct 'NestedInB' is not available due to missing import of defining module 'members_B'}}
     _ = NestedInC.self
-    _ = AmbiguousNestedType.self
+    _ = AmbiguousNestedType.self // expected-ambiguity-error{{ambiguous use of 'AmbiguousNestedType'}}
   }
 
   var hasNestedInAType: NestedInA { fatalError() }
diff --git a/validation-test/Sema/rdar84879566.swift b/validation-test/Sema/rdar84879566.swift
index a4d1e24b42ec5..9c9a1ba7a0dc3 100644
--- a/validation-test/Sema/rdar84879566.swift
+++ b/validation-test/Sema/rdar84879566.swift
@@ -20,6 +20,6 @@ struct TupleBuilder {
 
 struct MyApp: Tupled {
   var tuple: some Any {
-    MyView() // expected-error {{ambiguous use of 'init()'}}
+    MyView() // expected-error {{ambiguous use of 'MyView'}}
   }
 }
diff --git a/validation-test/compiler_crashers_fixed/issue-85364.swift b/validation-test/compiler_crashers_fixed/issue-85364.swift
index ce66778201aab..e4290d48174cc 100644
--- a/validation-test/compiler_crashers_fixed/issue-85364.swift
+++ b/validation-test/compiler_crashers_fixed/issue-85364.swift
@@ -9,7 +9,7 @@ struct S1 {  // expected-note {{found this candidate}} \
   var c: () -> Void
 }
 
-S1 {}  // expected-error {{ambiguous use of 'init'}}
+S1 {}  // expected-error {{ambiguous use of 'S1'}}
 
 struct S1 {  // expected-note {{found this candidate}} \
              // expected-error {{invalid redeclaration of 'S1'}}