diff --git a/setup/build.py b/setup/build.py
index 6d8cbf45e1..e4978258dd 100644
--- a/setup/build.py
+++ b/setup/build.py
@@ -49,10 +49,12 @@ class Extension:
         self.libraries = d['libraries'] = kwargs.get('libraries', [])
         self.cflags = d['cflags'] = kwargs.get('cflags', [])
         self.uses_icu = 'icuuc' in self.libraries
+        if self.needs_cxx and kwargs.get('needs_c++'):
+            std_prefix = '/std:' if iswindows else '-std='
+            self.cflags.insert(0, std_prefix + 'c++' + kwargs['needs_c++'])
+
         if iswindows:
             self.cflags.append('/DCALIBRE_MODINIT_FUNC=PyMODINIT_FUNC')
-            if self.needs_cxx and kwargs.get('needs_c++14'):
-                self.cflags.insert(0, '/std:c++14')
         else:
             return_type = 'PyObject*'
             extern_decl = 'extern "C"' if self.needs_cxx else ''
@@ -61,14 +63,8 @@ class Extension:
                 '-DCALIBRE_MODINIT_FUNC='
                 '{} __attribute__ ((visibility ("default"))) {}'.format(extern_decl, return_type))
 
-            if self.needs_cxx:
-                if kwargs.get('needs_c++11'):
-                    self.cflags.insert(0, '-std=c++11')
-                elif kwargs.get('needs_c++14'):
-                    self.cflags.insert(0, '-std=c++14')
-            else:
-                if kwargs.get('needs_c99'):
-                    self.cflags.insert(0, '-std=c99')
+            if kwargs.get('needs_c'):
+                self.cflags.insert(0, '-std=c' + kwargs['needs_c'])
 
         self.ldflags = d['ldflags'] = kwargs.get('ldflags', [])
         self.optional = d['options'] = kwargs.get('optional', False)
@@ -182,6 +178,20 @@ def get_python_include_paths():
 is_macos_universal_build = ismacos and 'universal2' in sysconfig.get_platform()
 
 
+def basic_windows_flags(debug=False):
+    cflags = '/c /nologo /W3 /EHsc /utf-8'.split()
+    cflags.append('/Zi' if debug else '/DNDEBUG')
+    suffix = ('d' if debug else '')
+    cflags.append('/MD' + suffix)
+    ldflags = f'/DLL /nologo /INCREMENTAL:NO /NODEFAULTLIB:libcmt{suffix}.lib'.split()
+    if debug:
+        ldflags.append('/DEBUG')
+    # cflags = '/c /nologo /Ox /MD /W3 /EHsc /Zi'.split()
+    # ldflags = '/DLL /nologo /INCREMENTAL:NO /DEBUG'.split()
+    cflags.append('/GS-')
+    return cflags, ldflags
+
+
 def init_env(debug=False, sanitize=False):
     from setup.build_environment import win_ld, win_inc, win_lib, NMAKE, win_cc
     linker = None
@@ -236,17 +246,7 @@ def init_env(debug=False, sanitize=False):
 
     if iswindows:
         cc = cxx = win_cc
-        cflags = '/c /nologo /W3 /EHsc /utf-8'.split()
-        cflags.append('/Zi' if debug else '/DNDEBUG')
-        suffix = ('d' if debug else '')
-        cflags.append('/MD' + suffix)
-        ldflags = f'/DLL /nologo /INCREMENTAL:NO /NODEFAULTLIB:libcmt{suffix}.lib'.split()
-        if debug:
-            ldflags.append('/DEBUG')
-        # cflags = '/c /nologo /Ox /MD /W3 /EHsc /Zi'.split()
-        # ldflags = '/DLL /nologo /INCREMENTAL:NO /DEBUG'.split()
-        cflags.append('/GS-')
-
+        cflags, ldflags = basic_windows_flags(debug)
         for p in win_inc:
             cflags.append('-I'+p)
         for p in win_lib:
diff --git a/setup/extensions.json b/setup/extensions.json
index 6eae64d0d3..fc3b7aa55f 100644
--- a/setup/extensions.json
+++ b/setup/extensions.json
@@ -6,7 +6,7 @@
         "lib_dirs": "!hunspell_lib_dirs",
         "libraries": "hunspell-1.7",
         "windows_libraries": "libhunspell",
-		"needs_c++11": true
+		"needs_c++": "11"
     },
     {
         "name": "hyphen",
@@ -14,7 +14,7 @@
 		"libraries": "hyphen",
         "inc_dirs": "!hyphen_inc_dirs",
         "lib_dirs": "!hyphen_lib_dirs",
-		"needs_c99": true
+		"needs_c": "99"
     },
     {
         "name": "uchardet",
@@ -27,7 +27,7 @@
         "name": "unicode_names",
         "headers": "unicode_names/names.h unicode_names/data-types.h",
         "sources": "unicode_names/unicode_names.c",
-        "needs_c99": true
+        "needs_c": "99"
     },
     {
         "name": "speedup",
@@ -82,7 +82,7 @@
         "name": "sqlite_extension",
         "headers": "calibre/utils/cpp_binding.h",
         "sources": "calibre/db/sqlite_extension.cpp",
-		"needs_c++14": true,
+		"needs_c++": "14",
         "libraries": "icudata icui18n icuuc icuio stemmer",
         "windows_libraries": "icudt icuin icuuc icuio libstemmer",
         "lib_dirs": "!icu_lib_dirs",
@@ -124,19 +124,19 @@
         "lib_dirs": "!podofo_lib",
         "inc_dirs": "!podofo_inc",
         "error": "!podofo_error",
-		"needs_c++11": true
+		"needs_c++": "11"
     },
     {
         "name": "html_as_json",
         "sources": "calibre/srv/html_as_json.cpp",
-		"needs_c++11": true
+		"needs_c++": "11"
     },
     {
         "name": "fast_css_transform",
         "headers": "calibre/utils/cpp_binding.h calibre/utils/stb_sprintf.h",
         "sources": "calibre/srv/fast_css_transform.cpp",
 		"inc_dirs": "perfect-hashing",
-		"needs_c++14": true
+		"needs_c++": "14"
     },
     {
         "name": "rcc_backend",
@@ -190,7 +190,8 @@
         "headers": "calibre/utils/cpp_binding.h calibre/utils/windows/common.h",
         "sources": "calibre/utils/windows/winspeech.cpp",
         "libraries": "WindowsApp",
-        "cflags": "/X /std:c++17 /Zc:__cplusplus /bigobj /await /permissive- /WX /Zc:twoPhase-"
+		"needs_c++": "17",
+        "cflags": "/X /Zc:__cplusplus /bigobj /await /permissive- /WX /Zc:twoPhase-"
     },
     {
         "name": "wpd",