diff --git a/mesonbuild/backend/xcodebackend.py b/mesonbuild/backend/xcodebackend.py
index bc66baf9d3ce..7c51ea548a98 100644
--- a/mesonbuild/backend/xcodebackend.py
+++ b/mesonbuild/backend/xcodebackend.py
@@ -1756,8 +1756,8 @@ def generate_single_build_target(self, objects_dict: PbxDict, target_name: str,
                         lang = 'cpp'
                     langs.add(lang)
                     langname = LANGNAMEMAP[lang]
-                    langargs.setdefault(langname, [])
-                    langargs[langname] = cargs + cti_args + args
+                    langargs.setdefault(langname, set())
+                    langargs[langname] |= set(cargs + cti_args + args)
             symroot = os.path.join(self.environment.get_build_dir(), target.subdir).rstrip('/')
             bt_dict = PbxDict()
             objects_dict.add_item(valid, bt_dict, buildtype)