diff --git a/stdlib/core/BridgeStorage.swift b/stdlib/core/BridgeStorage.swift
index 526eabf72fa..6d4b5506571 100644
--- a/stdlib/core/BridgeStorage.swift
+++ b/stdlib/core/BridgeStorage.swift
@@ -70,7 +70,7 @@ struct _BridgeStorage<
   mutating func isUniquelyReferencedNative() -> Bool {
     return _swift_isUniquelyReferencedNonObjC_nonNull_bridgeObject(
       _bitPattern(rawValue)
-    ) != 0
+    )
   }
 
   public // @testable
@@ -110,7 +110,7 @@ struct _BridgeStorage<
     _sanityCheck(isNative)
     _sanityCheck(_nonPointerBits(rawValue) == 0)
     let p: UnsafePointer<HeapObject> = Builtin.reinterpretCast(rawValue)
-    return _swift_isUniquelyReferenced_nonNull_native(p) != 0
+    return _swift_isUniquelyReferenced_nonNull_native(p)
   }
 
   public // @testable
diff --git a/stdlib/core/Builtin.swift b/stdlib/core/Builtin.swift
index 2f3ba41b1a7..135e911369a 100644
--- a/stdlib/core/Builtin.swift
+++ b/stdlib/core/Builtin.swift
@@ -241,7 +241,7 @@ internal func _usesNativeSwiftReferenceCounting(theClass: AnyClass) -> Bool {
 #if _runtime(_ObjC)
   return _swift_usesNativeSwiftReferenceCounting_class(
     unsafeAddressOf(theClass)
-  ) != 0
+  )
 #else
   return true
 #endif
diff --git a/stdlib/core/HashedCollections.swift.gyb b/stdlib/core/HashedCollections.swift.gyb
index bbc919fea93..ee012dc30e8 100644
--- a/stdlib/core/HashedCollections.swift.gyb
+++ b/stdlib/core/HashedCollections.swift.gyb
@@ -2551,7 +2551,7 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorageType {
       let o: UnsafePointer<HeapObject> = Builtin.reinterpretCast(self)
       let result = _swift_isUniquelyReferenced_native(o)
       Builtin.fixLifetime(self)
-      return result != 0
+      return result
     }
 
     switch self {
@@ -2559,7 +2559,7 @@ internal enum _Variant${Self}Storage<${TypeParametersDecl}> : _HashStorageType {
       let o: UnsafePointer<HeapObject> = Builtin.reinterpretCast(self)
       let result = _swift_isUniquelyReferenced_native(o)
       Builtin.fixLifetime(self)
-      return result != 0
+      return result
     case .Cocoa:
       // Don't consider Cocoa storage mutable, even if it is mutable and is
       // uniquely referenced.
diff --git a/stdlib/core/HeapBuffer.swift b/stdlib/core/HeapBuffer.swift
index 4c68d0482f0..080ca4ce9e2 100644
--- a/stdlib/core/HeapBuffer.swift
+++ b/stdlib/core/HeapBuffer.swift
@@ -70,7 +70,7 @@ internal func _isUniquelyReferenced_native(
   inout x: Builtin.NativeObject?
 ) -> Bool {
   let p: UnsafePointer<_HeapObject> = Builtin.reinterpretCast(x)
-  let result = _swift_isUniquelyReferenced_native(p) != 0
+  let result = _swift_isUniquelyReferenced_native(p)
   Builtin.fixLifetime(x)
   return result
 }
@@ -216,7 +216,7 @@ internal struct _HeapBuffer<Value, Element> : Equatable {
     let o: UnsafePointer<HeapObject> = Builtin.reinterpretCast(_storage)
     let result = _swift_isUniquelyReferenced_native(o)
     Builtin.fixLifetime(_storage)
-    return result != 0
+    return result
   }
 }
 
diff --git a/stdlib/core/ManagedBuffer.swift b/stdlib/core/ManagedBuffer.swift
index fbd2852805f..c8ea4689159 100644
--- a/stdlib/core/ManagedBuffer.swift
+++ b/stdlib/core/ManagedBuffer.swift
@@ -263,7 +263,7 @@ public struct ManagedBufferPointer<Value, Element> : Equatable {
     let o = UnsafePointer<HeapObject>(Builtin.bridgeToRawPointer(_nativeBuffer))
     let result = _swift_isUniquelyReferenced_nonNull_native(o)
     _fixLifetime(_nativeBuffer)
-    return result != 0
+    return result
   }
   
   //===--- internal/private API -------------------------------------------===//
@@ -414,7 +414,7 @@ public func isUniquelyReferencedNonObjC<T: AnyObject>(inout object: T) -> Bool {
   let o = UnsafePointer<Void>(Builtin.bridgeToRawPointer(object))
   let result = _swift_isUniquelyReferencedNonObjC_nonNull(o)
   Builtin.fixLifetime(object)
-  return result != 0
+  return result
 }
 
 /// Returns `true` iff `object` is a non-\ `@objc` class instance with a single
@@ -447,7 +447,7 @@ public func isUniquelyReferenced<T: NonObjectiveCBase>(
   let o = UnsafePointer<HeapObject>(Builtin.bridgeToRawPointer(object))
   let result = _swift_isUniquelyReferenced_nonNull_native(o)
   Builtin.fixLifetime(object)
-  return result != 0
+  return result
 }
 
 /// Returns `true` iff `object` is a non-\ `@objc` class instance with
@@ -482,6 +482,6 @@ public func isUniquelyReferencedNonObjC<T: AnyObject>(
   let o = Builtin.reinterpretCast(object) as UnsafePointer<Void>
   let result = _swift_isUniquelyReferencedNonObjC(o)
   Builtin.fixLifetime(object)
-  return result != 0
+  return result
 }
 
diff --git a/stdlib/core/Shims.swift b/stdlib/core/Shims.swift
index e823bb893a3..075566deb15 100644
--- a/stdlib/core/Shims.swift
+++ b/stdlib/core/Shims.swift
@@ -40,7 +40,7 @@ internal func _isUniquelyReferenced_native(
   inout x: Builtin.NativeObject
 ) -> Bool {
   let p = UnsafePointer<_HeapObject>(Builtin.bridgeToRawPointer(x))
-  let result = _swift_isUniquelyReferenced_nonNull_native(p) != 0
+  let result = _swift_isUniquelyReferenced_nonNull_native(p)
   Builtin.fixLifetime(x)
   return result
 }
diff --git a/stdlib/runtime/SwiftObject.mm b/stdlib/runtime/SwiftObject.mm
index 4cdc0a460dc..e43232642e5 100644
--- a/stdlib/runtime/SwiftObject.mm
+++ b/stdlib/runtime/SwiftObject.mm
@@ -446,7 +446,7 @@ bool swift::usesNativeSwiftReferenceCounting(const ClassMetadata *theClass) {
 }
 
 // version for SwiftShims
-unsigned char
+bool
 swift::_swift_usesNativeSwiftReferenceCounting_class(const void *theClass) {
 #if SWIFT_OBJC_INTEROP
   return usesNativeSwiftReferenceCounting((const ClassMetadata *)theClass);
@@ -935,7 +935,7 @@ extern "C" const char *swift_getGenericClassObjCName(const ClassMetadata *clas,
 
 // Given a non-nil object reference, return true iff the object uses
 // native swift reference counting.
-unsigned char swift::_swift_usesNativeSwiftReferenceCounting_nonNull(
+bool swift::_swift_usesNativeSwiftReferenceCounting_nonNull(
   const void* object
 ) {
     assert(object != nullptr);
@@ -949,7 +949,7 @@ unsigned char swift::_swift_usesNativeSwiftReferenceCounting_nonNull(
 
 // Given a non-nil non-@objc object reference, return true iff the
 // object has a strong reference count of 1.
-unsigned char swift::_swift_isUniquelyReferenced_nonNull_native(
+bool swift::_swift_isUniquelyReferenced_nonNull_native(
   const HeapObject* object
 ) {
   assert(object != nullptr);
@@ -959,7 +959,7 @@ unsigned char swift::_swift_isUniquelyReferenced_nonNull_native(
 
 // Given a non-@objc object reference, return true iff the
 // object is non-nil and has a strong reference count of 1.
-unsigned char swift::_swift_isUniquelyReferenced_native(
+bool swift::_swift_isUniquelyReferenced_native(
   const HeapObject* object
 ) {
   return object != nullptr
@@ -968,7 +968,7 @@ unsigned char swift::_swift_isUniquelyReferenced_native(
 
 // Given a non-nil object reference, return true iff the object is a
 // native swift object with strong reference count of 1.
-unsigned char swift::_swift_isUniquelyReferencedNonObjC_nonNull(
+bool swift::_swift_isUniquelyReferencedNonObjC_nonNull(
   const void* object
 ) {
   assert(object != nullptr);
@@ -981,22 +981,18 @@ unsigned char swift::_swift_isUniquelyReferencedNonObjC_nonNull(
 
 // Given an object reference, return true iff it is non-nil and refers
 // to a native swift object with strong reference count of 1.
-unsigned char swift::_swift_isUniquelyReferencedNonObjC(
+bool swift::_swift_isUniquelyReferencedNonObjC(
   const void* object
 ) {
   return object != nullptr
     && _swift_isUniquelyReferencedNonObjC_nonNull(object);
 }
 
-//===----------------------------------------------------------------------===//
-// FIXME: this should return bool but it chokes the compiler
-// <rdar://problem/18573806>
-//===----------------------------------------------------------------------===//
 /// Given the bits of a possibly-nil Native swift object reference, or of a
 /// word-sized Swift enum containing a Native swift object reference as
 /// a payload, return true iff the object's strong reference count is
 /// 1.
-unsigned char swift::_swift_isUniquelyReferenced_native_spareBits(
+bool swift::_swift_isUniquelyReferenced_native_spareBits(
   __swift_uintptr_t bits
 ) {
   const auto object = reinterpret_cast<HeapObject*>(
@@ -1012,7 +1008,7 @@ unsigned char swift::_swift_isUniquelyReferenced_native_spareBits(
 
 /// Return true if the given bits of a Builtin.BridgeObject refer to a
 /// native swift object whose strong reference count is 1.
-unsigned char swift::_swift_isUniquelyReferencedNonObjC_nonNull_bridgeObject(
+bool swift::_swift_isUniquelyReferencedNonObjC_nonNull_bridgeObject(
   __swift_uintptr_t bits
 ) {
   auto bridgeObject = (void*)bits;
diff --git a/stdlib/shims/RuntimeShims.h b/stdlib/shims/RuntimeShims.h
index b3ae52ce260..ba44fb62485 100644
--- a/stdlib/shims/RuntimeShims.h
+++ b/stdlib/shims/RuntimeShims.h
@@ -23,18 +23,20 @@
 
 #ifdef __cplusplus
 namespace swift { extern "C" {
+#else
+#define bool _Bool
 #endif
 
-unsigned char _swift_isUniquelyReferencedNonObjC(const void *);
-unsigned char _swift_isUniquelyReferencedNonObjC_nonNull(const void *);
-unsigned char _swift_usesNativeSwiftReferenceCounting_nonNull(const void *);
-unsigned char _swift_usesNativeSwiftReferenceCounting_class(const void *);
-unsigned char _swift_isUniquelyReferenced_native_spareBits(__swift_uintptr_t bits);
-unsigned char _swift_isUniquelyReferencedNonObjC_nonNull_bridgeObject(
+bool _swift_isUniquelyReferencedNonObjC(const void *);
+bool _swift_isUniquelyReferencedNonObjC_nonNull(const void *);
+bool _swift_usesNativeSwiftReferenceCounting_nonNull(const void *);
+bool _swift_usesNativeSwiftReferenceCounting_class(const void *);
+bool _swift_isUniquelyReferenced_native_spareBits(__swift_uintptr_t bits);
+bool _swift_isUniquelyReferencedNonObjC_nonNull_bridgeObject(
   __swift_uintptr_t bits);
-unsigned char
+bool
 _swift_isUniquelyReferenced_nonNull_native(const struct HeapObject *);
-unsigned char _swift_isUniquelyReferenced_native(const struct HeapObject *);
+bool _swift_isUniquelyReferenced_native(const struct HeapObject *);
 __swift_size_t _swift_class_getInstancePositiveExtentSize(const void *);
 
 #ifdef __cplusplus