diff --git a/pyproject.toml b/pyproject.toml
index 3d6cbc975..3ca84a620 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -155,8 +155,10 @@ wheel_build_env = ".pkg"
 constrain_package_deps = true
 use_frozen_constraints = true
 dependency_groups = ["tests"]
+set_env.PYTHONDEVMODE = "1"
+set_env.PYTHONWARNINGS = "error::BytesWarning"
 commands = [[
-    "pytest", "-v", "--tb=short", "--basetemp={env_tmp_dir}",
+    "python", "-bb", "-m", "pytest", "-v", "--tb=short", "--basetemp={env_tmp_dir}",
     {replace = "posargs", default = [], extend = true},
 ]]
 
diff --git a/src/click/parser.py b/src/click/parser.py
index 1ea1f7166..fb8247d2d 100644
--- a/src/click/parser.py
+++ b/src/click/parser.py
@@ -325,8 +325,8 @@ def _process_args_for_options(self, state: _ParsingState) -> None:
             arg = state.rargs.pop(0)
             arglen = len(arg)
             # Double dashes always handled explicitly regardless of what
-            # prefixes are valid.
-            if arg == "--":
+            # prefixes are valid. Handle both bytes and string to avoid BytesWarning.
+            if arg == b"--" if isinstance(arg, bytes) else arg == "--":
                 return
             elif arg[:1] in self._opt_prefixes and arglen > 1:
                 self._process_opts(arg, state)
diff --git a/src/click/types.py b/src/click/types.py
index e71c1c21e..388959bc4 100644
--- a/src/click/types.py
+++ b/src/click/types.py
@@ -972,8 +972,11 @@ def convert(
         ctx: Context | None,
     ) -> str | bytes | os.PathLike[str]:
         rv = value
-
-        is_dash = self.file_okay and self.allow_dash and rv in (b"-", "-")
+        # Use simple string comparison instead of `rv in (b"-", "-")` to avoid
+        # BytesWarning when Python runs with -bb flag (which treats bytes/str
+        # comparison as an error). The input type is str | os.PathLike[str],
+        # so bytes are not expected here.
+        is_dash = self.file_okay and self.allow_dash and rv == "-"
 
         if not is_dash:
             if self.resolve_path:
diff --git a/tests/test_types.py b/tests/test_types.py
index 75434f104..507e686d7 100644
--- a/tests/test_types.py
+++ b/tests/test_types.py
@@ -251,6 +251,30 @@ def test_invalid_path_with_esc_sequence():
     assert "my\\ndir" in exc_info.value.message
 
 
+def test_path_allow_dash_no_bytes_warning():
+    """Test that Path(allow_dash=True).convert() doesn't raise BytesWarning.
+
+    This verifies the fix for issue #2877. The original code used
+    `rv in (b"-", "-")` which causes BytesWarning with python -bb flag.
+    Now we use simple `rv == "-"` comparison.
+    """
+    import warnings
+
+    path_type = click.Path(allow_dash=True)
+
+    # Verify dash handling works without BytesWarning when -bb flag is used
+    with warnings.catch_warnings():
+        warnings.simplefilter("error", BytesWarning)
+        result = path_type.convert("-", None, None)
+        assert result == "-"
+
+    # Also verify regular paths work fine
+    with warnings.catch_warnings():
+        warnings.simplefilter("error", BytesWarning)
+        result = path_type.convert("test.txt", None, None)
+        assert result == "test.txt"
+
+
 def test_choice_get_invalid_choice_message():
     choice = click.Choice(["a", "b", "c"])
     message = choice.get_invalid_choice_message("d", ctx=None)