diff --git a/tornado/options.py b/tornado/options.py
index 7ebae719f..fdfaea424 100644
--- a/tornado/options.py
+++ b/tornado/options.py
@@ -640,22 +640,19 @@ def _parse_datetime(self, value: str) -> datetime.datetime:
     )
 
     def _parse_timedelta(self, value: str) -> datetime.timedelta:
-        try:
-            sum = datetime.timedelta()
-            start = 0
-            while start < len(value):
-                m = self._TIMEDELTA_PATTERN.match(value, start)
-                if not m:
-                    raise Exception()
-                num = float(m.group(1))
-                units = m.group(2) or "seconds"
-                units = self._TIMEDELTA_ABBREV_DICT.get(units, units)
-
-                sum += datetime.timedelta(**{units: num})
-                start = m.end()
-            return sum
-        except Exception:
-            raise
+        sum = datetime.timedelta()
+        start = 0
+        while start < len(value):
+            m = self._TIMEDELTA_PATTERN.match(value, start)
+            if not m:
+                raise Error("Invalid time delta: %r" % value)
+            num = float(m.group(1))
+            units = m.group(2) or "seconds"
+            units = self._TIMEDELTA_ABBREV_DICT.get(units, units)
+
+            sum += datetime.timedelta(**{units: num})
+            start = m.end()
+        return sum
 
     def _parse_bool(self, value: str) -> bool:
         return value.lower() not in ("false", "0", "f")
diff --git a/tornado/test/options_test.py b/tornado/test/options_test.py
index 6c76da364..b193c0adf 100644
--- a/tornado/test/options_test.py
+++ b/tornado/test/options_test.py
@@ -254,6 +254,15 @@ def test_multiple_int(self):
         options.parse_command_line(["main.py", "--foo=1,3,5:7"])
         self.assertEqual(options.foo, [1, 3, 5, 6, 7])
 
+    def test_parse_timedelta_invalid_raises_options_error(self):
+        # Malformed timedelta input should raise options.Error with a
+        # human-readable message, not a bare Exception with no context.
+        options = OptionParser()
+        options.define("foo", type=datetime.timedelta)
+        with self.assertRaises(Error) as cm:
+            options.parse_command_line(["main.py", "--foo=xyz"])
+        self.assertIn("xyz", str(cm.exception))
+
     def test_error_redefine(self):
         options = OptionParser()
         options.define("foo")