diff --git a/esphome/platformio/extra_script.py b/esphome/platformio/extra_script.py
index 4c4c716009..a88201266d 100644
--- a/esphome/platformio/extra_script.py
+++ b/esphome/platformio/extra_script.py
@@ -110,6 +110,11 @@ class _FakeSConsEnv:
     def get(self, key: str, default: str | None = None) -> str | None:
         return self._vars.get(key, default)
 
+    def __getitem__(self, key: str) -> str:
+        # Scripts also read env["BOARD_MCU"]; without this the broad
+        # handler would discard every flag the script captured
+        return self._vars[key]
+
     def Append(self, **kwargs) -> None:  # noqa: N802 (SCons API name)
         for key, value in kwargs.items():
             if key not in _CAPTURED_KEYS:
diff --git a/tests/unit_tests/test_platformio_extra_script.py b/tests/unit_tests/test_platformio_extra_script.py
index d09f02d95f..73523f4bc0 100644
--- a/tests/unit_tests/test_platformio_extra_script.py
+++ b/tests/unit_tests/test_platformio_extra_script.py
@@ -169,6 +169,22 @@ def test_apply_extra_script_callable_target_and_str_flags(tmp_path) -> None:
     assert c.data["build"]["flags"] == ["-DBASE=1", "-lesp8266"]
 
 
+def test_apply_extra_script_subscript_env_read(tmp_path) -> None:
+    """Scripts also read env["BOARD_MCU"]; the subscript form must work or
+    the broad handler discards every flag the script captured."""
+    (tmp_path / "src").mkdir()
+    script = tmp_path / "extra.py"
+    script.write_text("env.Append(LIBS=[env['BOARD_MCU']])\n")
+
+    c = IDFComponent("owner/name", "1.0", source=URLSource("http://dummy"))
+    c.path = tmp_path
+    c.data = {"build": {"extraScript": "extra.py"}}
+
+    apply_extra_script(c, board_mcu=lambda: "esp8266", pio_platform="espressif8266")
+
+    assert c.data["build"]["flags"] == ["-lesp8266"]
+
+
 def test_apply_extra_script_no_script_and_no_flags(tmp_path) -> None:
 
     # No extraScript declared: nothing happens, the target is never resolved
diff --git a/tests/unit_tests/test_platformio_library.py b/tests/unit_tests/test_platformio_library.py
index 6726df2e4b..25d074e26f 100644
--- a/tests/unit_tests/test_platformio_library.py
+++ b/tests/unit_tests/test_platformio_library.py
@@ -162,9 +162,13 @@ def caplog_at_info():
     handler.emit = records.append
     logger = logging.getLogger("esphome.platformio.library")
     logger.addHandler(handler)
+    # The level must actually admit INFO or the no-INFO assertions are vacuous
+    old_level = logger.level
+    logger.setLevel(logging.INFO)
     try:
         yield records
     finally:
+        logger.setLevel(old_level)
         logger.removeHandler(handler)