diff --git a/backend/app/services/espidf_compiler.py b/backend/app/services/espidf_compiler.py
index ecb6efbb..49abe6dd 100644
--- a/backend/app/services/espidf_compiler.py
+++ b/backend/app/services/espidf_compiler.py
@@ -2735,7 +2735,7 @@ class ESPIDFCompiler:
                         progress_callback, normalized_opts, spiffs_files,
                         allowed_libraries=allowed, libraries_dir=scope_dir,
                         arduino_mode=arduino_mode, use_idf5=use_idf5,
-                        pure_idf=pure_idf,
+                        pure_idf=pure_idf, board_fqbn=board_fqbn,
                     )
                 with tempfile.TemporaryDirectory(prefix='espidf_') as temp_dir:
                     project_dir = Path(temp_dir) / 'project'
@@ -2746,7 +2746,7 @@ class ESPIDFCompiler:
                         progress_callback, normalized_opts, spiffs_files,
                         allowed_libraries=allowed, libraries_dir=scope_dir,
                         arduino_mode=arduino_mode, use_idf5=use_idf5,
-                        pure_idf=pure_idf,
+                        pure_idf=pure_idf, board_fqbn=board_fqbn,
                     )
             finally:
                 if scope_dir is not None:
@@ -2809,6 +2809,7 @@ class ESPIDFCompiler:
         arduino_mode: Optional[bool] = None,
         use_idf5: Optional[bool] = None,
         pure_idf: bool = False,
+        board_fqbn: str | None = None,
     ) -> dict:
         """Inner compile body: writes sketch + libs into `project_dir`,
         runs cmake + ninja, merges binaries. Caller is responsible for
@@ -2862,7 +2863,7 @@ class ESPIDFCompiler:
         # file instead of an env var makes it a configure dependency: CMake
         # re-runs when it changes, env vars it silently ignores.
         board_cmake_lines = ['# generated by espidf_compiler — do not edit']
-        if arduino_mode and not pure_idf:
+        if arduino_mode and not pure_idf and board_fqbn:
             flags = self._arduino_board_flags(board_fqbn)
             if flags['board']:
                 macro = re.sub(r'[^A-Z0-9_]', '_', str(flags['board']).upper())