Index: lib/Support/Unix/Memory.inc
===================================================================
--- lib/Support/Unix/Memory.inc
+++ lib/Support/Unix/Memory.inc
@@ -153,7 +153,14 @@
 
   int Protect = getPosixProtectionFlags(Flags);
 
-  int Result = ::mprotect((void*)((uintptr_t)M.Address & ~(PageSize-1)), PageSize*((M.Size+PageSize-1)/PageSize), Protect);
+  uintptr_t start = (uintptr_t)M.Address;
+  uintptr_t end = start + M.Size;
+  // Round down the start address to a page boundary
+  start = start & ~(PageSize - 1);
+  // Round up the end address to a page boundary
+  end = (end + PageSize - 1) & ~(PageSize - 1);
+  int Result = ::mprotect((void*)start, end - start, Protect);
+
   if (Result != 0)
     return std::error_code(errno, std::generic_category());