diff --git a/src/tyro/_backends/_tyro_backend.py b/src/tyro/_backends/_tyro_backend.py
index 0f4dafba..0eb823ad 100644
--- a/src/tyro/_backends/_tyro_backend.py
+++ b/src/tyro/_backends/_tyro_backend.py
@@ -328,7 +328,6 @@ def _recurse(
                         add_help=add_help,
                         console_outputs=console_outputs,
                         seen_double_dash=True,
-                        return_unknown_args=return_unknown_args,
                     )
                     continue
 
@@ -484,7 +483,6 @@ def _recurse(
                         local_prog,
                         add_help=add_help,
                         console_outputs=console_outputs,
-                        return_unknown_args=return_unknown_args,
                         min_remaining_positional=self._min_positional_consumption(
                             positional_args
                         ),
@@ -544,7 +542,6 @@ def _recurse(
                         local_prog,
                         add_help=add_help,
                         console_outputs=console_outputs,
-                        return_unknown_args=return_unknown_args,
                     )
                     continue
 
@@ -796,7 +793,6 @@ def _consume_argument(
         add_help: bool,
         console_outputs: bool,
         seen_double_dash: bool = False,
-        return_unknown_args: bool = False,
         min_remaining_positional: int = 0,
     ):
         arg_values: list[str] = []
@@ -838,13 +834,12 @@ def _consume_argument(
                         break
 
                     # To match argparse behavior, any flag-like string
-                    # terminates when return_unknown_args is set. We check
-                    # for a leading alpha character after stripping dashes
-                    # to avoid treating negative numbers (like -2 or -3.14)
+                    # terminates positional nargs consumption. We check for
+                    # a leading alpha character after stripping dashes to
+                    # avoid treating negative numbers (like -2 or -3.14)
                     # as flags.
                     if (
-                        return_unknown_args
-                        and token_key.startswith("-")
+                        token_key.startswith("-")
                         and len(token_key) > 1
                         and token_key.lstrip("-")[:1].isalpha()
                     ):
diff --git a/tests/test_positional.py b/tests/test_positional.py
index f7f0f240..dc49697f 100644
--- a/tests/test_positional.py
+++ b/tests/test_positional.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import pathlib
 from dataclasses import dataclass
 from typing import List, Optional, Sequence, Tuple
 
@@ -373,3 +374,21 @@ class Config:
     result = tyro.cli(Config, args=["-x", "a", "--", "b", "c"])
     assert result.pos == ("b", "c")
     assert result.var_len == ("a",)
+
+
+def test_positional_varlen_rejects_unknown_flags() -> None:
+    """Regression test for #457: unknown flags should not be consumed as positional values.
+
+    With tyro >= 1.0.9, --invalid was incorrectly accepted as a positional
+    path value instead of raising an unrecognized-options error.
+    """
+
+    @dataclass
+    class Arguments:
+        logfile_paths: tyro.conf.Positional[tuple[pathlib.Path, ...]]
+        cfg_file: Annotated[pathlib.Path, tyro.conf.arg(aliases=["-c"])] = pathlib.Path(
+            "config.yaml"
+        )
+
+    with pytest.raises(SystemExit):
+        tyro.cli(Arguments, args=["--invalid"])
diff --git a/tests/test_py311_generated/test_positional_generated.py b/tests/test_py311_generated/test_positional_generated.py
index 47019da2..8cd9b90a 100644
--- a/tests/test_py311_generated/test_positional_generated.py
+++ b/tests/test_py311_generated/test_positional_generated.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import pathlib
 from dataclasses import dataclass
 from typing import Annotated, List, Optional, Sequence, Tuple
 
@@ -372,3 +373,21 @@ class Config:
     result = tyro.cli(Config, args=["-x", "a", "--", "b", "c"])
     assert result.pos == ("b", "c")
     assert result.var_len == ("a",)
+
+
+def test_positional_varlen_rejects_unknown_flags() -> None:
+    """Regression test for #457: unknown flags should not be consumed as positional values.
+
+    With tyro >= 1.0.9, --invalid was incorrectly accepted as a positional
+    path value instead of raising an unrecognized-options error.
+    """
+
+    @dataclass
+    class Arguments:
+        logfile_paths: tyro.conf.Positional[tuple[pathlib.Path, ...]]
+        cfg_file: Annotated[pathlib.Path, tyro.conf.arg(aliases=["-c"])] = pathlib.Path(
+            "config.yaml"
+        )
+
+    with pytest.raises(SystemExit):
+        tyro.cli(Arguments, args=["--invalid"])