diff --git a/Include/pystate.h b/Include/pystate.h
index bc1e23e39c7..b9008432114 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -148,7 +148,7 @@ typedef struct {
        Incremented by the -d command line option. Set by the PYTHONDEBUG
        environment variable. If set to -1 (default), inherit Py_DebugFlag
        value. */
-    int debug;
+    int parser_debug;
 
     /* If equal to 0, Python won't try to write ``.pyc`` files on the
        import of source modules.
@@ -185,13 +185,13 @@ typedef struct {
       !Py_NoUserSiteDirectory. */
     int user_site_directory;
 
-    /* If greater than 0, enable unbuffered mode: force the stdout and stderr
+    /* If equal to 0, enable unbuffered mode: force the stdout and stderr
        streams to be unbuffered.
 
-       Set to 1 by the -u option. Set by the PYTHONUNBUFFERED environment
-       variable. If set to -1 (default), inherit Py_UnbufferedStdioFlag
-       value. */
-    int unbuffered_stdio;
+       Set to 0 by the -u option. Set by the PYTHONUNBUFFERED environment
+       variable.
+       If set to -1 (default), it is set to !Py_UnbufferedStdioFlag. */
+    int buffered_stdio;
 
 #ifdef MS_WINDOWS
     /* If greater than 1, use the "mbcs" encoding instead of the UTF-8
@@ -268,12 +268,12 @@ typedef struct {
         .inspect = -1, \
         .interactive = -1, \
         .optimization_level = -1, \
-        .debug= -1, \
+        .parser_debug= -1, \
         .write_bytecode = -1, \
         .verbose = -1, \
         .quiet = -1, \
         .user_site_directory = -1, \
-        .unbuffered_stdio = -1, \
+        .buffered_stdio = -1, \
         _PyCoreConfig_WINDOWS_INIT \
         ._install_importlib = 1, \
         ._frozen = -1}
diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index dd7d273629b..79622f15945 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -280,12 +280,12 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         'inspect': 0,
         'interactive': 0,
         'optimization_level': 0,
-        'debug': 0,
+        'parser_debug': 0,
         'write_bytecode': 1,
         'verbose': 0,
         'quiet': 0,
         'user_site_directory': 1,
-        'unbuffered_stdio': 0,
+        'buffered_stdio': 1,
 
         '_install_importlib': 1,
         '_check_hash_pycs_mode': 'default',
@@ -328,7 +328,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'write_bytecode': 0,
             'verbose': 1,
             'quiet': 1,
-            'unbuffered_stdio': 1,
+            'buffered_stdio': 0,
             'utf8_mode': 1,
             'user_site_directory': 0,
             '_frozen': 1,
@@ -361,7 +361,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'write_bytecode': 0,
             'verbose': 1,
             'quiet': 1,
-            'unbuffered_stdio': 1,
+            'buffered_stdio': 0,
             'user_site_directory': 0,
             'faulthandler': 1,
 
@@ -384,7 +384,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'pycache_prefix': 'env_pycache_prefix',
             'write_bytecode': 0,
             'verbose': 1,
-            'unbuffered_stdio': 1,
+            'buffered_stdio': 0,
             'user_site_directory': 0,
             'faulthandler': 1,
             'dev_mode': 1,
diff --git a/Modules/main.c b/Modules/main.c
index f0b811b5628..aef821fe93c 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -565,10 +565,9 @@ _PyCoreConfig_GetGlobalConfig(_PyCoreConfig *config)
     COPY_FLAG(inspect, Py_InspectFlag);
     COPY_FLAG(interactive, Py_InteractiveFlag);
     COPY_FLAG(optimization_level, Py_OptimizeFlag);
-    COPY_FLAG(debug, Py_DebugFlag);
+    COPY_FLAG(parser_debug, Py_DebugFlag);
     COPY_FLAG(verbose, Py_VerboseFlag);
     COPY_FLAG(quiet, Py_QuietFlag);
-    COPY_FLAG(unbuffered_stdio, Py_UnbufferedStdioFlag);
 #ifdef MS_WINDOWS
     COPY_FLAG(legacy_windows_fs_encoding, Py_LegacyWindowsFSEncodingFlag);
     COPY_FLAG(legacy_windows_stdio, Py_LegacyWindowsStdioFlag);
@@ -576,6 +575,7 @@ _PyCoreConfig_GetGlobalConfig(_PyCoreConfig *config)
     COPY_FLAG(_frozen, Py_FrozenFlag);
 
     COPY_NOT_FLAG(use_environment, Py_IgnoreEnvironmentFlag);
+    COPY_NOT_FLAG(buffered_stdio, Py_UnbufferedStdioFlag);
     COPY_NOT_FLAG(site_import, Py_NoSiteFlag);
     COPY_NOT_FLAG(write_bytecode, Py_DontWriteBytecodeFlag);
     COPY_NOT_FLAG(user_site_directory, Py_NoUserSiteDirectory);
@@ -608,16 +608,16 @@ _PyCoreConfig_SetGlobalConfig(const _PyCoreConfig *config)
     COPY_FLAG(inspect, Py_InspectFlag);
     COPY_FLAG(interactive, Py_InteractiveFlag);
     COPY_FLAG(optimization_level, Py_OptimizeFlag);
-    COPY_FLAG(debug, Py_DebugFlag);
+    COPY_FLAG(parser_debug, Py_DebugFlag);
     COPY_FLAG(verbose, Py_VerboseFlag);
     COPY_FLAG(quiet, Py_QuietFlag);
-    COPY_FLAG(unbuffered_stdio, Py_UnbufferedStdioFlag);
 #ifdef MS_WINDOWS
     COPY_FLAG(legacy_windows_fs_encoding, Py_LegacyWindowsFSEncodingFlag);
     COPY_FLAG(legacy_windows_stdio, Py_LegacyWindowsStdioFlag);
 #endif
 
     COPY_NOT_FLAG(use_environment, Py_IgnoreEnvironmentFlag);
+    COPY_NOT_FLAG(buffered_stdio, Py_UnbufferedStdioFlag);
     COPY_NOT_FLAG(site_import, Py_NoSiteFlag);
     COPY_NOT_FLAG(write_bytecode, Py_DontWriteBytecodeFlag);
     COPY_NOT_FLAG(user_site_directory, Py_NoUserSiteDirectory);
@@ -749,12 +749,12 @@ _PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
     COPY_ATTR(inspect);
     COPY_ATTR(interactive);
     COPY_ATTR(optimization_level);
-    COPY_ATTR(debug);
+    COPY_ATTR(parser_debug);
     COPY_ATTR(write_bytecode);
     COPY_ATTR(verbose);
     COPY_ATTR(quiet);
     COPY_ATTR(user_site_directory);
-    COPY_ATTR(unbuffered_stdio);
+    COPY_ATTR(buffered_stdio);
 #ifdef MS_WINDOWS
     COPY_ATTR(legacy_windows_fs_encoding);
     COPY_ATTR(legacy_windows_stdio);
@@ -990,7 +990,7 @@ pymain_parse_cmdline_impl(_PyMain *pymain, _PyCoreConfig *config,
             break;
 
         case 'd':
-            config->debug++;
+            config->parser_debug++;
             break;
 
         case 'i':
@@ -1029,7 +1029,7 @@ pymain_parse_cmdline_impl(_PyMain *pymain, _PyCoreConfig *config,
             break;
 
         case 'u':
-            config->unbuffered_stdio = 1;
+            config->buffered_stdio = 0;
             break;
 
         case 'v':
@@ -1287,7 +1287,7 @@ pymain_init_stdio(_PyMain *pymain, _PyCoreConfig *config)
     _setmode(fileno(stderr), O_BINARY);
 #endif
 
-    if (config->unbuffered_stdio) {
+    if (!config->buffered_stdio) {
 #ifdef HAVE_SETVBUF
         setvbuf(stdin,  (char *)NULL, _IONBF, BUFSIZ);
         setvbuf(stdout, (char *)NULL, _IONBF, BUFSIZ);
@@ -1905,7 +1905,7 @@ config_read_env_vars(_PyCoreConfig *config)
     assert(config->use_environment > 0);
 
     /* Get environment variables */
-    get_env_flag(config, &config->debug, "PYTHONDEBUG");
+    get_env_flag(config, &config->parser_debug, "PYTHONDEBUG");
     get_env_flag(config, &config->verbose, "PYTHONVERBOSE");
     get_env_flag(config, &config->optimization_level, "PYTHONOPTIMIZE");
     get_env_flag(config, &config->inspect, "PYTHONINSPECT");
@@ -1922,7 +1922,12 @@ config_read_env_vars(_PyCoreConfig *config)
         config->user_site_directory = 0;
     }
 
-    get_env_flag(config, &config->unbuffered_stdio, "PYTHONUNBUFFERED");
+    int unbuffered_stdio = 0;
+    get_env_flag(config, &unbuffered_stdio, "PYTHONUNBUFFERED");
+    if (unbuffered_stdio) {
+        config->buffered_stdio = 0;
+    }
+
 #ifdef MS_WINDOWS
     get_env_flag(config, &config->legacy_windows_fs_encoding,
                  "PYTHONLEGACYWINDOWSFSENCODING");
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 94db29b8d80..1cdc4c3648f 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -356,13 +356,13 @@ dump_config(void)
     printf("inspect = %i\n", config->inspect);
     printf("interactive = %i\n", config->interactive);
     printf("optimization_level = %i\n", config->optimization_level);
-    printf("debug = %i\n", config->debug);
+    printf("parser_debug = %i\n", config->parser_debug);
     printf("write_bytecode = %i\n", config->write_bytecode);
     printf("verbose = %i\n", config->verbose);
     ASSERT_EQUAL(config->verbose, Py_VerboseFlag);
     printf("quiet = %i\n", config->quiet);
     printf("user_site_directory = %i\n", config->user_site_directory);
-    printf("unbuffered_stdio = %i\n", config->unbuffered_stdio);
+    printf("buffered_stdio = %i\n", config->buffered_stdio);
     /* FIXME: test legacy_windows_fs_encoding */
     /* FIXME: test legacy_windows_stdio */
 
@@ -509,7 +509,7 @@ static int test_init_from_config(void)
     Py_OptimizeFlag = 1;
     config.optimization_level = 2;
 
-    /* FIXME: test debug */
+    /* FIXME: test parser_debug */
 
     putenv("PYTHONDONTWRITEBYTECODE=");
     Py_DontWriteBytecodeFlag = 0;
@@ -520,7 +520,7 @@ static int test_init_from_config(void)
 
     putenv("PYTHONUNBUFFERED=");
     Py_UnbufferedStdioFlag = 0;
-    config.unbuffered_stdio = 1;
+    config.buffered_stdio = 0;
 
     putenv("PYTHONNOUSERSITE=");
     Py_NoUserSiteDirectory = 0;