diff --git a/src/click/core.py b/src/click/core.py
index f0a624be3..1eafd4695 100644
--- a/src/click/core.py
+++ b/src/click/core.py
@@ -2897,7 +2897,11 @@ def get_default(
         # (instead of eagerly in __init__) prevents callable flag_values
         # (like classes) from being instantiated by the callable check below.
         # https://github.com/pallets/click/issues/3121
-        if value is True and self.is_flag:
+        # Skip the conversion when flag_value is explicitly False (a negative flag).
+        # For negative flags, default=True is the literal default value — not a signal
+        # to activate the flag. Converting it to False would silently override the
+        # user's explicit default. https://github.com/pallets/click/issues/3111
+        if value is True and self.is_flag and self.flag_value is not False:
             value = self.flag_value
         elif call and callable(value):
             value = value()
diff --git a/tests/test_options.py b/tests/test_options.py
index e335f3c1a..ab1eb66e2 100644
--- a/tests/test_options.py
+++ b/tests/test_options.py
@@ -1435,13 +1435,13 @@ def test_type_from_flag_value():
         # Not passing --foo returns the default value as-is, in its Python type, then
         # converted by the option type.
         ({"type": bool, "default": True, "flag_value": True}, [], True),
-        ({"type": bool, "default": True, "flag_value": False}, [], False),
+        ({"type": bool, "default": True, "flag_value": False}, [], True),
         ({"type": bool, "default": False, "flag_value": True}, [], False),
         ({"type": bool, "default": False, "flag_value": False}, [], False),
         ({"type": bool, "default": None, "flag_value": True}, [], None),
         ({"type": bool, "default": None, "flag_value": False}, [], None),
         ({"type": str, "default": True, "flag_value": True}, [], "True"),
-        ({"type": str, "default": True, "flag_value": False}, [], "False"),
+        ({"type": str, "default": True, "flag_value": False}, [], "True"),
         ({"type": str, "default": False, "flag_value": True}, [], "False"),
         ({"type": str, "default": False, "flag_value": False}, [], "False"),
         ({"type": str, "default": "foo", "flag_value": True}, [], "foo"),
@@ -1480,6 +1480,31 @@ def cmd(foo):
     assert result.output == repr(expected)
 
 
+def test_negative_flag_with_true_default(runner):
+    """A negative flag (flag_value=False, default=True) should return True when not
+    passed and False when passed. Regression test for https://github.com/pallets/click/issues/3111."""
+
+    @click.command()
+    @click.option(
+        "--without-xyz",
+        "enable_xyz",
+        flag_value=False,
+        default=True,
+    )
+    def cmd(enable_xyz):
+        click.echo(repr(enable_xyz), nl=False)
+
+    result = runner.invoke(cmd, [])
+    assert result.output == "True", (
+        "default=True should be returned when flag is not passed"
+    )
+
+    result = runner.invoke(cmd, ["--without-xyz"])
+    assert result.output == "False", (
+        "flag_value=False should be returned when flag is passed"
+    )
+
+
 @pytest.mark.parametrize(
     ("args", "opts"),
     [
diff --git a/tests/test_termui.py b/tests/test_termui.py
index 8220431bb..7f0881779 100644
--- a/tests/test_termui.py
+++ b/tests/test_termui.py
@@ -604,9 +604,9 @@ def cmd(arg1):
     ({"prompt": True, "default": True, "flag_value": True}, [], "[Y/n]", "", True),
     ({"prompt": True, "default": True, "flag_value": True}, [], "[Y/n]", "y", True),
     ({"prompt": True, "default": True, "flag_value": True}, [], "[Y/n]", "n", False),
-    ({"prompt": True, "default": True, "flag_value": False}, [], "[y/N]", "", False),
-    ({"prompt": True, "default": True, "flag_value": False}, [], "[y/N]", "y", True),
-    ({"prompt": True, "default": True, "flag_value": False}, [], "[y/N]", "n", False),
+    ({"prompt": True, "default": True, "flag_value": False}, [], "[Y/n]", "", True),
+    ({"prompt": True, "default": True, "flag_value": False}, [], "[Y/n]", "y", True),
+    ({"prompt": True, "default": True, "flag_value": False}, [], "[Y/n]", "n", False),
     # default=False
     ({"prompt": True, "default": False, "flag_value": True}, [], "[y/N]", "", False),
     ({"prompt": True, "default": False, "flag_value": True}, [], "[y/N]", "y", True),