diff --git a/src/lib_c/x86_64-windows-msvc/c/winbase.cr b/src/lib_c/x86_64-windows-msvc/c/winbase.cr
index 82af52a8775a..6fb4c3620bf0 100644
--- a/src/lib_c/x86_64-windows-msvc/c/winbase.cr
+++ b/src/lib_c/x86_64-windows-msvc/c/winbase.cr
@@ -13,9 +13,8 @@ lib LibC
   FORMAT_MESSAGE_FROM_SYSTEM     = 0x00001000_u32
   FORMAT_MESSAGE_ARGUMENT_ARRAY  = 0x00002000_u32
 
-  # TODO: Use LPWSTR
-  fun FormatMessageA(dwFlags : DWORD, lpSource : Void*, dwMessageId : DWORD, dwLanguageId : DWORD,
-                     lpBuffer : LPSTR, nSize : DWORD, arguments : Void*) : DWORD
+  fun FormatMessageW(dwFlags : DWORD, lpSource : Void*, dwMessageId : DWORD, dwLanguageId : DWORD,
+                     lpBuffer : LPWSTR, nSize : DWORD, arguments : Void*) : DWORD
 
   struct FILETIME
     dwLowDateTime : DWORD
diff --git a/src/winerror.cr b/src/winerror.cr
index 6d011a654212..c52af4fc5d07 100644
--- a/src/winerror.cr
+++ b/src/winerror.cr
@@ -8,9 +8,9 @@ class WinError < Errno
   end
 
   def initialize(message, code)
-    buffer = uninitialized UInt8[256]
-    size = LibC.FormatMessageA(LibC::FORMAT_MESSAGE_FROM_SYSTEM, nil, code, 0, buffer, buffer.size, nil)
-    details = String.new(buffer.to_unsafe, size).strip
+    buffer = uninitialized UInt16[256]
+    size = LibC.FormatMessageW(LibC::FORMAT_MESSAGE_FROM_SYSTEM, nil, code, 0, buffer, buffer.size, nil)
+    details = String.from_utf16(buffer.to_slice[0, size]).strip
     super("#{message}: [WinError #{code}, #{details}]", winerror_to_errno(code))
   end