Index: include/llvm/Support/FileSystem.h
===================================================================
--- include/llvm/Support/FileSystem.h
+++ include/llvm/Support/FileSystem.h
@@ -745,7 +745,7 @@
 
 private:
   /// Platform-specific mapping state.
-  uint64_t Size;
+  size_t Size;
   void *Mapping;
 
   std::error_code init(int FD, uint64_t Offset, mapmode Mode);
@@ -763,7 +763,7 @@
 
   ~mapped_file_region();
 
-  uint64_t size() const;
+  size_t size() const;
   char *data() const;
 
   /// Get a const view of the data. Modifying this memory has undefined
Index: lib/Support/Unix/Path.inc
===================================================================
--- lib/Support/Unix/Path.inc
+++ lib/Support/Unix/Path.inc
@@ -641,15 +641,9 @@
   return std::error_code();
 }
 
-mapped_file_region::mapped_file_region(int fd, mapmode mode, uint64_t length,
+mapped_file_region::mapped_file_region(int fd, mapmode mode, size_t length,
                                        uint64_t offset, std::error_code &ec)
     : Size(length), Mapping() {
-  // Make sure that the requested size fits within SIZE_T.
-  if (length > std::numeric_limits<size_t>::max()) {
-    ec = make_error_code(errc::invalid_argument);
-    return;
-  }
-
   ec = init(fd, offset, mode);
   if (ec)
     Mapping = nullptr;