diff --git a/esphome/arduino8266/component.py b/esphome/arduino8266/component.py
index 94d008374c..6365a26dda 100644
--- a/esphome/arduino8266/component.py
+++ b/esphome/arduino8266/component.py
@@ -16,7 +16,6 @@ from __future__ import annotations
 from dataclasses import dataclass, field
 import logging
 from pathlib import Path
-import shlex
 
 from esphome.core import CORE, Library
 from esphome.espidf.extra_script import apply_extra_script
@@ -36,6 +35,7 @@ from esphome.platformio.library import (
     lib_ignore_set,
     normalize_dependencies,
     parse_library_properties,
+    split_flag_entry,
 )
 
 _LOGGER = logging.getLogger(__name__)
@@ -79,7 +79,7 @@ def _library_info(name: str, read_path: Path, data: dict) -> ArduinoLibrary:
         (
             token
             for entry in ensure_list(build.get("flags", []))
-            for token in shlex.split(entry)
+            for token in split_flag_entry(entry, f"library {name}")
         ),
         f"library {name}",
     )
diff --git a/esphome/build_gen/arduino8266.py b/esphome/build_gen/arduino8266.py
index cbb09057f2..e5af8cc1c4 100644
--- a/esphome/build_gen/arduino8266.py
+++ b/esphome/build_gen/arduino8266.py
@@ -19,7 +19,6 @@ import logging
 import os
 from pathlib import Path
 import re
-import shlex
 import subprocess
 import sys
 
@@ -40,7 +39,7 @@ from esphome.const import KEY_CORE, KEY_FRAMEWORK_VERSION
 from esphome.core import CORE, EsphomeError
 from esphome.framework_helpers import get_project_cxx_compile_flags
 from esphome.helpers import mkdir_p, write_file_if_changed
-from esphome.platformio.library import join_flag_args
+from esphome.platformio.library import join_flag_args, split_flag_entry
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -179,7 +178,7 @@ def _flag_defines() -> dict[str, str]:
         # Shell-lex multi-token entries the way PlatformIO does, so a knob
         # in "-DKNOB -DOTHER" is still detected; single tokens pass verbatim
         # to keep any quoting in their bodies intact.
-        for tok in shlex.split(flag) if " " in flag else (flag,):
+        for tok in split_flag_entry(flag, "esphome") if " " in flag else (flag,):
             if tok.startswith("-D"):
                 body = tok[2:]
                 defines[body.split("=", 1)[0]] = body
@@ -319,7 +318,7 @@ def _project_flags() -> tuple[list[str], list[str], list[Path], list[str]]:
         # they do under PlatformIO. Other entries pass verbatim: lexing them
         # would strip the quotes in defines like -DBOARD="...".
         tokens = (
-            join_flag_args(shlex.split(flag), "esphome")
+            join_flag_args(split_flag_entry(flag, "esphome"), "esphome")
             if flag.startswith(("-L", "-l"))
             else [flag]
         )
diff --git a/esphome/espidf/component.py b/esphome/espidf/component.py
index 1c951ae274..68c9398e19 100644
--- a/esphome/espidf/component.py
+++ b/esphome/espidf/component.py
@@ -28,6 +28,7 @@ from esphome.platformio.library import (
     convert_libraries,
     ensure_list,
     join_flag_args,
+    split_flag_entry,
     split_list_by_condition,
 )
 
@@ -62,10 +63,6 @@ def generate_cmakelists_txt(component: IDFComponent) -> str:
     Returns:
         str: The complete CMakeLists.txt content as a string
     """
-    # Late import: this module loads with the esp32 platform on every
-    # validate/compile, but shlex is only needed when generating component
-    # CMakeLists.
-    import shlex
 
     def escape_entry(p: PathType) -> str:
         # In CMakeLists.txt, backslashes need to be escaped
@@ -107,7 +104,11 @@ def generate_cmakelists_txt(component: IDFComponent) -> str:
     # -I/-L/-l tokens re-glue to their argument ("-I foo" -> "-Ifoo") so the
     # prefix classifiers below still route them.
     build_flags = join_flag_args(
-        (token for entry in build_flags for token in shlex.split(entry)),
+        (
+            token
+            for entry in build_flags
+            for token in split_flag_entry(entry, f"library {component.name}")
+        ),
         f"library {component.name}",
     )
 
diff --git a/esphome/platformio/library.py b/esphome/platformio/library.py
index 5c936c280f..c1e659e0f6 100644
--- a/esphome/platformio/library.py
+++ b/esphome/platformio/library.py
@@ -553,6 +553,16 @@ def _resolve_registry_version(
     return owner, name, best["name"], pkgfile["download_url"]
 
 
+def split_flag_entry(entry: str, owner: str) -> list[str]:
+    """``shlex.split`` with a clean error naming the offending flags entry."""
+    import shlex
+
+    try:
+        return shlex.split(entry)
+    except ValueError as err:
+        raise EsphomeError(f"Malformed build flag {entry!r} in {owner}: {err}") from err
+
+
 def join_flag_args(tokens: Iterable[str], owner: str) -> list[str]:
     """Join a bare ``-I``/``-L``/``-l`` with its following token (PIO lexing)."""
     out: list[str] = []
diff --git a/tests/unit_tests/test_platformio_library.py b/tests/unit_tests/test_platformio_library.py
index 0eede78656..6c7f6d6462 100644
--- a/tests/unit_tests/test_platformio_library.py
+++ b/tests/unit_tests/test_platformio_library.py
@@ -531,3 +531,12 @@ def test_convert_libraries_skips_incompatible_dependency(tmp_path, monkeypatch):
     top = convert_libraries([Library("esphome/A", "1.0.0", None)], _backend())
 
     assert top[0].dependencies == []
+
+
+def test_split_flag_entry_unbalanced_quote_is_clean() -> None:
+    """A malformed flags entry raises EsphomeError, not a raw ValueError."""
+    from esphome.platformio.library import split_flag_entry
+
+    assert split_flag_entry('-DX="a b"', "library x") == ["-DX=a b"]
+    with pytest.raises(EsphomeError, match=r"Malformed build flag.*library x"):
+        split_flag_entry('-DX="unclosed', "library x")