diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index cfcd2212cfaf..417b2c6af7a3 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -193,11 +193,11 @@ set(ENABLE_X86_RELAX_RELOCATIONS OFF CACHE BOOL
     "enable x86 relax relocations by default")
 
 set(CLANG_DEFAULT_CXX_STDLIB "" CACHE STRING
-  "Default C++ stdlib to use (empty for architecture default, \"libstdc++\" or \"libc++\"")
+  "Default C++ stdlib to use (empty for platform default, \"libstdc++\" or \"libc++\"")
 if (NOT(CLANG_DEFAULT_CXX_STDLIB STREQUAL "" OR
         CLANG_DEFAULT_CXX_STDLIB STREQUAL "libstdc++" OR
         CLANG_DEFAULT_CXX_STDLIB STREQUAL "libc++"))
-  message(WARNING "Resetting default C++ stdlib to use architecture default")
+  message(WARNING "Resetting default C++ stdlib to use platform default")
   set(CLANG_DEFAULT_CXX_STDLIB "")
 endif()
 
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index b4491d6a5562..66b76cda14a7 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -577,6 +577,8 @@ ToolChain::CXXStdlibType ToolChain::GetCXXStdlibType(const ArgList &Args) const{
         << A->getAsString(Args);
   }
 
+  // If no argument was provided or its value was invalid, look for the
+  // default unless forced or configured to take the platform default.
   if (!HasValidType && (ForcePlatformDefault ||
       !ParseCXXStdlibType(CLANG_DEFAULT_CXX_STDLIB, Type)))
     Type = GetDefaultCXXStdlibType();