--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -494,38 +494,34 @@ def check_compiler(compiler, language, t
     # Note: We do a strict version check because there sometimes are backwards
     # incompatible changes in the standard, and not all code that compiles as
     # C99 compiles as e.g. C11 (as of writing, this is true of libnestegg, for
     # example)
     if info.language == 'C' and info.language_version != 199901:
         if info.type in ('clang-cl', 'clang', 'gcc'):
             append_flag('-std=gnu99')
 
-    # Note: MSVC, while supporting C++11, still reports 199711L for __cplusplus.
+    # Note: MSVC, while supporting C++14, still reports 199711L for __cplusplus.
     # Note: this is a strict version check because we used to always add
-    # -std=gnu++11.
+    # -std=gnu++14.
     draft_cxx14_version = 201300
     cxx14_version = 201402
     if info.language == 'C++':
-        if target.kernel != 'WINNT':
-            if info.type in ('clang', 'gcc') and info.language_version != 201103:
-                append_flag('-std=gnu++11')
-        else:
-            if info.type == 'clang' and info.language_version != 201103:
-                append_flag('-std=gnu++11')
-            # MSVC 2015 headers include C++14 features, but don't guard them
-            # with appropriate checks.
-            if info.type == 'clang-cl' and info.language_version != cxx14_version:
-                append_flag('-std=c++14')
-            # GCC 4.9 indicates that it implements draft C++14 features
-            # instead of the full language.
-            elif info.type == 'gcc' and not \
-                (info.language_version == draft_cxx14_version or
-                 info.language_version == cxx14_version):
-                append_flag('-std=gnu++14')
+        if info.type == 'clang' and info.language_version != cxx14_version:
+            append_flag('-std=gnu++14')
+        # MSVC 2015 headers include C++14 features, but don't guard them
+        # with appropriate checks.
+        elif info.type == 'clang-cl' and info.language_version != cxx14_version:
+            append_flag('-std=c++14')
+        # GCC 4.9 indicates that it implements draft C++14 features
+        # instead of the full language.
+        elif info.type == 'gcc' and \
+                info.language_version not in (draft_cxx14_version,
+                                              cxx14_version):
+            append_flag('-std=gnu++14')
 
     # We force clang-cl to emulate Visual C++ 2017 version 15.4
     if info.type == 'clang-cl' and info.version != '19.11.25547':
         # This flag is a direct clang-cl flag that doesn't need -Xclang,
         # add it directly.
         flags.append('-fms-compatibility-version=19.11.25547')
 
     # Check compiler target

--- a/python/mozbuild/mozbuild/test/configure/test_toolchain_configure.py
+++ b/python/mozbuild/mozbuild/test/configure/test_toolchain_configure.py
@@ -83,16 +83,20 @@ def GCC(version):
 @memoize
 def GXX(version):
     return GCC_BASE(version) + DEFAULT_CXX_97 + SUPPORTS_GNUXX11
 
 SUPPORTS_DRAFT_CXX14_VERSION = {
     '-std=gnu++14': DRAFT_CXX_14,
 }
 
+SUPPORTS_DRAFT_CXX14_VERSION = {
+    '-std=gnu++14': DRAFT_CXX_14,
+}
+
 GCC_4_7 = GCC('4.7.3')
 GXX_4_7 = GXX('4.7.3')
 GCC_4_9 = GCC('4.9.3')
 GXX_4_9 = GXX('4.9.3') + SUPPORTS_DRAFT_CXX14_VERSION
 GCC_5 = GCC('5.2.1') + DEFAULT_C11
 GXX_5 = GXX('5.2.1') + SUPPORTS_GNUXX14
 
 GCC_PLATFORM_LITTLE_ENDIAN = {
@@ -428,31 +432,31 @@ class LinuxToolchainTest(BaseToolchainTe
     GCC_4_9_RESULT = CompilerResult(
         flags=['-std=gnu99'],
         version='4.9.3',
         type='gcc',
         compiler='/usr/bin/gcc',
         language='C',
     )
     GXX_4_9_RESULT = CompilerResult(
-        flags=['-std=gnu++11'],
+        flags=['-std=gnu++14'],
         version='4.9.3',
         type='gcc',
         compiler='/usr/bin/g++',
         language='C++',
     )
     GCC_5_RESULT = CompilerResult(
         flags=['-std=gnu99'],
         version='5.2.1',
         type='gcc',
         compiler='/usr/bin/gcc-5',
         language='C',
     )
     GXX_5_RESULT = CompilerResult(
-        flags=['-std=gnu++11'],
+        flags=['-std=gnu++14'],
         version='5.2.1',
         type='gcc',
         compiler='/usr/bin/g++-5',
         language='C++',
     )
     CLANG_3_3_RESULT = CompilerResult(
         flags=[],
         version='3.3.0',
@@ -464,17 +468,17 @@ class LinuxToolchainTest(BaseToolchainTe
     CLANG_3_6_RESULT = CompilerResult(
         flags=['-std=gnu99'],
         version='3.6.2',
         type='clang',
         compiler='/usr/bin/clang',
         language='C',
     )
     CLANGXX_3_6_RESULT = CompilerResult(
-        flags=['-std=gnu++11'],
+        flags=['-std=gnu++14'],
         version='3.6.2',
         type='clang',
         compiler='/usr/bin/clang++',
         language='C++',
     )
 
     def test_gcc(self):
         # We'll try gcc and clang, and find gcc first.