diff --git a/src/click/parser.py b/src/click/parser.py
index 8ea69acda..f9ec1a20d 100644
--- a/src/click/parser.py
+++ b/src/click/parser.py
@@ -398,7 +398,7 @@ def _match_short_opt(self, arg: str, state: _ParsingState) -> None:
                 if self.ignore_unknown_options:
                     unknown_options.append(ch)
                     continue
-                raise NoSuchOption(opt, ctx=self.ctx)
+                raise NoSuchOption(arg, ctx=self.ctx)
             if option.takes_value:
                 # Any characters left in arg?  Pretend they're the
                 # next arg, and stop consuming characters of arg.
diff --git a/tests/test_options.py b/tests/test_options.py
index 50992e2d1..b4d7ae4af 100644
--- a/tests/test_options.py
+++ b/tests/test_options.py
@@ -144,6 +144,19 @@ def cli():
     assert f"No such option '{unknown_flag}'." in result.output
 
 
+def test_unknown_multichar_short_option_shows_full_name(runner):
+    """Error message should show the full option string, not just the first char."""
+
+    @click.command()
+    def cli():
+        pass
+
+    result = runner.invoke(cli, ["-dbg"])
+    assert result.exception
+    assert "No such option '-dbg'." in result.output
+    assert "No such option '-d'." not in result.output
+
+
 @pytest.mark.parametrize(
     ("value", "expect"),
     [