--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -88,7 +88,7 @@ int Py_BytesWarningFlag; /* Warn on str(
 int Py_UseClassExceptionsFlag = 1; /* Needed by bltinmodule.c: deprecated */
 int Py_FrozenFlag; /* Needed by getpath.c */
 int Py_IgnoreEnvironmentFlag; /* e.g. PYTHONPATH, PYTHONHOME */
-int Py_DontWriteBytecodeFlag; /* Suppress writing bytecode files (*.pyc) */
+int Py_DontWriteBytecodeFlag = 1; /* Suppress writing bytecode files (*.pyc) */
 int Py_NoUserSiteDirectory = 0; /* for -s and site.py */
 int Py_UnbufferedStdioFlag = 0; /* Unbuffered binary std{in,out,err} */
 int Py_HashRandomizationFlag = 0; /* for -R and PYTHONHASHSEED */
@@ -329,7 +329,7 @@ _Py_InitializeEx_Private(int install_sig
     if ((p = Py_GETENV("PYTHONOPTIMIZE")) && *p != '\0')
         Py_OptimizeFlag = add_flag(Py_OptimizeFlag, p);
     if ((p = Py_GETENV("PYTHONDONTWRITEBYTECODE")) && *p != '\0')
-        Py_DontWriteBytecodeFlag = add_flag(Py_DontWriteBytecodeFlag, p);
+        Py_DontWriteBytecodeFlag = atoi(p);
     /* The variable is only tested for existence here; _PyRandom_Init will
        check its value further. */
     if ((p = Py_GETENV("PYTHONHASHSEED")) && *p != '\0')