diff -rupN a/stdlib/public/stubs/UnicodeNormalization.cpp b/stdlib/public/stubs/UnicodeNormalization.cpp
--- a/stdlib/public/stubs/UnicodeNormalization.cpp	2017-05-02 15:42:43.465819610 -0700
+++ b/stdlib/public/stubs/UnicodeNormalization.cpp	2017-05-02 15:46:47.788404828 -0700
@@ -86,11 +86,7 @@ private:
     for (unsigned char c = 0; c < 128; ++c) {
       UErrorCode ErrorCode = U_ZERO_ERROR;
       intptr_t NumCollationElts = 0;
-#if defined(__CYGWIN__) || defined(_MSC_VER)
       UChar Buffer[1];
-#else
-      uint16_t Buffer[1];
-#endif
       Buffer[0] = c;
 
       UCollationElements *CollationIterator =
@@ -127,18 +123,12 @@ swift::_swift_stdlib_unicode_compare_utf
                                                  int32_t LeftLength,
                                                  const uint16_t *RightString,
                                                  int32_t RightLength) {
-#if defined(__CYGWIN__) || defined(_MSC_VER)
-  // ICU UChar type is platform dependent. In Cygwin, it is defined
-  // as wchar_t which size is 2. It seems that the underlying binary
+  // ICU UChar type is always char16_t as of ICU 59.
+  // It seems that the underlying binary
   // representation is same with swift utf16 representation.
   return ucol_strcoll(GetRootCollator(),
     reinterpret_cast<const UChar *>(LeftString), LeftLength,
     reinterpret_cast<const UChar *>(RightString), RightLength);
-#else
-  return ucol_strcoll(GetRootCollator(),
-    LeftString, LeftLength,
-    RightString, RightLength);
-#endif
 }
 
 /// Compares the strings via the Unicode Collation Algorithm on the root locale.
@@ -156,12 +146,8 @@ swift::_swift_stdlib_unicode_compare_utf
   UErrorCode ErrorCode = U_ZERO_ERROR;
 
   uiter_setUTF8(&LeftIterator, reinterpret_cast<const char *>(LeftString), LeftLength);
-#if defined(__CYGWIN__) || defined(_MSC_VER)
   uiter_setString(&RightIterator, reinterpret_cast<const UChar *>(RightString),
                   RightLength);
-#else
-  uiter_setString(&RightIterator, RightString, RightLength);
-#endif
 
   uint32_t Diff = ucol_strcollIter(GetRootCollator(),
     &LeftIterator, &RightIterator, &ErrorCode);
@@ -199,14 +185,9 @@ swift::_swift_stdlib_unicode_compare_utf
 void *swift::_swift_stdlib_unicodeCollationIterator_create(
     const __swift_uint16_t *Str, __swift_uint32_t Length) {
   UErrorCode ErrorCode = U_ZERO_ERROR;
-#if defined(__CYGWIN__) || defined(_MSC_VER)
   UCollationElements *CollationIterator = ucol_openElements(
     GetRootCollator(), reinterpret_cast<const UChar *>(Str), Length,
     &ErrorCode);
-#else
-  UCollationElements *CollationIterator = ucol_openElements(
-    GetRootCollator(), Str, Length, &ErrorCode);
-#endif
   if (U_FAILURE(ErrorCode)) {
     swift::crash("_swift_stdlib_unicodeCollationIterator_create: ucol_openElements() failed.");
   }
@@ -244,17 +225,11 @@ swift::_swift_stdlib_unicode_strToUpper(
                                         const uint16_t *Source,
                                         int32_t SourceLength) {
   UErrorCode ErrorCode = U_ZERO_ERROR;
-#if defined(__CYGWIN__) || defined(_MSC_VER)
   uint32_t OutputLength = u_strToUpper(reinterpret_cast<UChar *>(Destination),
                                        DestinationCapacity,
                                        reinterpret_cast<const UChar *>(Source),
                                        SourceLength,
                                        "", &ErrorCode);
-#else
-  uint32_t OutputLength = u_strToUpper(Destination, DestinationCapacity,
-                                       Source, SourceLength,
-                                       "", &ErrorCode);
-#endif
   if (U_FAILURE(ErrorCode) && ErrorCode != U_BUFFER_OVERFLOW_ERROR) {
     swift::crash("u_strToUpper: Unexpected error uppercasing unicode string.");
   }
@@ -271,17 +246,11 @@ swift::_swift_stdlib_unicode_strToLower(
                                         const uint16_t *Source,
                                         int32_t SourceLength) {
   UErrorCode ErrorCode = U_ZERO_ERROR;
-#if defined(__CYGWIN__) || defined(_MSC_VER)
   uint32_t OutputLength = u_strToLower(reinterpret_cast<UChar *>(Destination),
                                        DestinationCapacity,
                                        reinterpret_cast<const UChar *>(Source),
                                        SourceLength,
                                        "", &ErrorCode);
-#else
-  uint32_t OutputLength = u_strToLower(Destination, DestinationCapacity,
-                                       Source, SourceLength,
-                                       "", &ErrorCode);
-#endif
   if (U_FAILURE(ErrorCode) && ErrorCode != U_BUFFER_OVERFLOW_ERROR) {
     swift::crash("u_strToLower: Unexpected error lowercasing unicode string.");
   }