diff --git a/tests/functional2/lang/lang_util.py b/tests/functional2/lang/lang_util.py
index 66a5f6718..7302ab2e9 100644
--- a/tests/functional2/lang/lang_util.py
+++ b/tests/functional2/lang/lang_util.py
@@ -346,6 +346,7 @@ def _collect_generic_test_group(folder: Path) -> tuple[list[LangTest], list[Inva
     invalid_tests: list[InvalidLangTest] = []
     all_files = set(folder.iterdir())
     unused = {f.name for f in all_files if not f.name.startswith("_")}
+    collected: set[str] = set()
     for file in all_files:
         file: Path
         if file.suffix == ".exp":
@@ -356,6 +357,12 @@ def _collect_generic_test_group(folder: Path) -> tuple[list[LangTest], list[Inva
             # `"parse-fail-some-name.err.exp".stem` => "parse-fail-some-name.err"
             # `"parse-fail-some-name.err.exp".split(".")[0]` => "parse-fail-some-name"
             test_name = file.name.rsplit(".", 2)[0]
+            if test_name in collected:
+                # Skipping collection to avoid duplicate collection
+                # when both `.err.exp` and `.out.exp` are provided
+                # in case of non-error traces
+                continue
+            collected |= {test_name}
             full_name = LANG_TEST_ID_PATTERN.format(folder_name=parent_name, test_name=test_name)
             match = re.fullmatch(NAME_PATTERN_GENERIC_EXP, test_name)
             if match is None:
diff --git a/tests/functional2/lang/test_lang_infra.py b/tests/functional2/lang/test_lang_infra.py
index bf0a2816a..82f1bc73c 100644
--- a/tests/functional2/lang/test_lang_infra.py
+++ b/tests/functional2/lang/test_lang_infra.py
@@ -839,3 +839,23 @@ def test_generic_missing_in_file(pytest_command: Command):
     res = pytest_command.run().expect(1)
     out = res.stdout_plain
     assert "ERROR lang/test_lang.py::test_eval[generic-missing:eval-okay] - FileNotFound" in out
+
+
+@pytest.mark.parametrize("pytest_command", [["--setup-plan"]], indirect=True)
+@with_files(
+    get_functional2_lang_files(
+        {
+            "functional2": {
+                "lang": {
+                    "generic-duplicate": {
+                        "eval-okay.out.exp": File("A"),
+                        "eval-okay.err.exp": File("B"),
+                        "in.nix": File(""),
+                    }
+                }
+            }
+        }
+    )
+)
+def test_generic_no_duplicate_collection(pytest_command: Command):
+    pytest_command.run().ok()