--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -868,16 +868,30 @@ host_c_compiler = compiler('C', host, ot
 host_cxx_compiler = compiler('C++', host, c_compiler=host_c_compiler,
                              other_compiler=cxx_compiler,
                              other_c_compiler=c_compiler)
 
 # Generic compiler-based conditions.
 non_msvc_compiler = depends(c_compiler)(lambda info: info.type != 'msvc')
 building_with_gcc = depends(c_compiler)(lambda info: info.type == 'gcc')
 
+@depends(c_compiler)
+def msvs_version(info):
+    # clang-cl emulates the same version scheme as cl. And MSVS_VERSION needs to
+    # be set for GYP on Windows.
+    if info.type in ('clang-cl', 'msvc'):
+        if info.version >= '19.10':
+            return '2017'
+        elif info.version >= '19.00':
+            return '2015'
+
+    return ''
+
+set_config('MSVS_VERSION', msvs_version)
+
 include('compile-checks.configure')
 
 @depends(have_64_bit,
          try_compile(body='static_assert(sizeof(void *) == 8, "")',
                      check_msg='for 64-bit OS'))
 def check_have_64_bit(have_64_bit, compiler_have_64_bit):
     if have_64_bit != compiler_have_64_bit:
         configure_error('The target compiler does not agree with configure '

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -176,31 +176,29 @@ case "$target" in
 
         AC_DEFINE(_CRT_SECURE_NO_WARNINGS)
         AC_DEFINE(_CRT_NONSTDC_NO_WARNINGS)
         AC_DEFINE(_USE_MATH_DEFINES) # Otherwise MSVC's math.h doesn't #define M_PI.
 
         case "$CC_VERSION" in
         19*)
             _CC_SUITE=14
-            MSVS_VERSION=2015
             MSVC_C_RUNTIME_DLL=vcruntime140.dll
             MSVC_CXX_RUNTIME_DLL=msvcp140.dll
 
             # C5026: move constructor was implicitly defined as deleted
             CXXFLAGS="$CXXFLAGS -wd5026"
 
             # C5027: move assignment operator was implicitly defined as deleted
             CXXFLAGS="$CXXFLAGS -wd5027"
 
             # -Zc:sizedDealloc- disables C++14 global sized deallocation (see bug 1160146)
             CXXFLAGS="$CXXFLAGS -Zc:sizedDealloc-"
             ;;
         esac
-        AC_SUBST(MSVS_VERSION)
         AC_SUBST(MSVC_C_RUNTIME_DLL)
         AC_SUBST(MSVC_CXX_RUNTIME_DLL)
 
         # Check linker version
         _LD_FULL_VERSION=`"${LINK}" -v 2>&1 | sed -nre "$_MSVC_VER_FILTER"`
         _LD_MAJOR_VERSION=`echo ${_LD_FULL_VERSION} | $AWK -F\. '{ print $1 }'`
         if test "$_LD_MAJOR_VERSION" != "$_CC_SUITE"; then
             AC_MSG_ERROR([The linker major version, $_LD_FULL_VERSION,  does not match the compiler suite version, $_CC_SUITE.])

--- a/old-configure.in
+++ b/old-configure.in
@@ -233,17 +233,16 @@ case "$target" in
 
         AC_DEFINE(_CRT_SECURE_NO_WARNINGS)
         AC_DEFINE(_CRT_NONSTDC_NO_WARNINGS)
         AC_DEFINE(_USE_MATH_DEFINES) # Otherwise MSVC's math.h doesn't #define M_PI.
 
         case "$CC_VERSION" in
         19*)
             _CC_SUITE=14
-            MSVS_VERSION=2015
             MSVC_C_RUNTIME_DLL=vcruntime140.dll
             MSVC_CXX_RUNTIME_DLL=msvcp140.dll
 
             MOZ_CHECK_HEADER(dia2.h, MSVC_HAS_DIA_SDK=1)
             if test -n "$MSVC_HAS_DIA_SDK"; then
                 AC_DEFINE(MSVC_HAS_DIA_SDK)
             fi
 
@@ -270,17 +269,16 @@ case "$target" in
             if test -n "$WIN_UCRT_REDIST_DIR"; then
               if test ! -d "$WIN_UCRT_REDIST_DIR"; then
                 AC_MSG_ERROR([Invalid Windows UCRT Redist directory: ${WIN_UCRT_REDIST_DIR}])
               fi
               WIN_UCRT_REDIST_DIR=`cd "$WIN_UCRT_REDIST_DIR" && pwd -W`
             fi
             ;;
         esac
-        AC_SUBST(MSVS_VERSION)
         AC_SUBST(MSVC_HAS_DIA_SDK)
         AC_SUBST(MSVC_C_RUNTIME_DLL)
         AC_SUBST(MSVC_CXX_RUNTIME_DLL)
 
         AC_DEFINE(HAVE_SEH_EXCEPTIONS)
 
         if test -n "$WIN32_REDIST_DIR"; then
           if test ! -d "$WIN32_REDIST_DIR"; then

--- a/python/mozbuild/mozbuild/frontend/gyp_reader.py
+++ b/python/mozbuild/mozbuild/frontend/gyp_reader.py
@@ -5,16 +5,18 @@
 from __future__ import absolute_import, unicode_literals
 
 import gyp
 import gyp.msvs_emulation
 import sys
 import os
 import time
 import types
+import warnings
+
 import mozpack.path as mozpath
 from mozpack.files import FileFinder
 from .sandbox import alphabetical_sorted
 from .context import (
     ObjDirPath,
     SourcePath,
     TemplateContext,
     VARIABLES,
@@ -367,17 +369,24 @@ class GypProcessor(object):
 
         # gyp expects plain str instead of unicode. The frontend code gives us
         # unicode strings, so convert them.
         path = encode(path)
         if bool(config.substs['_MSC_VER']):
             # This isn't actually used anywhere in this generator, but it's needed
             # to override the registry detection of VC++ in gyp.
             os.environ['GYP_MSVS_OVERRIDE_PATH'] = 'fake_path'
-            os.environ['GYP_MSVS_VERSION'] = config.substs['MSVS_VERSION']
+
+            # TODO bug 1371485 upgrade vendored version of GYP to something that
+            # doesn't barf when MSVS_VERSION==2017.
+            msvs_version = config.substs['MSVS_VERSION']
+            if msvs_version == '2017':
+                warnings.warn('MSVS_VERSION being set to 2015 to appease GYP')
+                msvs_version = '2015'
+            os.environ['GYP_MSVS_VERSION'] = msvs_version
 
         params = {
             b'parallel': False,
             b'generator_flags': {},
             b'build_files': [path],
             b'root_targets': None,
         }