diff --git a/build/cmake/aom_configure.cmake b/build/cmake/aom_configure.cmake
index 33def6c..39e5c53 100644
--- a/build/cmake/aom_configure.cmake
+++ b/build/cmake/aom_configure.cmake
@@ -314,7 +314,12 @@
   endif()
 else()
   require_c_flag("-std=c99" YES)
-  if(WIN32 AND NOT MINGW)
+  if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang"
+     AND CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU"
+     AND CMAKE_CXX_SIMULATE_ID STREQUAL "MSVC")
+    # MSVC's STL requires C++14 as it's the compiler's default and minimum
+    # supported C++ version. However, clang (as opposed to clang-cl) in Visual
+    # Studio defaults to C++11.
     require_cxx_flag_nomsvc("-std=c++14" YES)
   else()
     require_cxx_flag_nomsvc("-std=c++11" YES)
diff --git a/build/cmake/aom_optimization.cmake b/build/cmake/aom_optimization.cmake
index f8eeb82..6b0c55a 100644
--- a/build/cmake/aom_optimization.cmake
+++ b/build/cmake/aom_optimization.cmake
@@ -46,7 +46,10 @@
   add_library(${target_name} OBJECT ${${sources}})
   set_property(TARGET ${target_name} PROPERTY FOLDER ${AOM_TARGET_CPU})
 
-  # Clang/CL requires the -mXXX flag. The MSVC version is not granular enough.
+  # MSVC does not need flags for intrinsics flavors other than AVX/AVX2.
+  # However, for clang-cl, the default is SSE2, and the MSVC frontend does not
+  # provide any flags to enable SSE3 up to SSE4.1. So we need to restrict the
+  # usage of MSVC-style flags to only the real MSVC.
   if(CMAKE_C_COMPILER_ID STREQUAL "MSVC")
     get_msvc_intrinsic_flag("${flag}" "flag")
   endif()