diff --git a/examples/calculator.py b/examples/calculator.py
index 60d982f96..e42273fe0 100644
--- a/examples/calculator.py
+++ b/examples/calculator.py
@@ -28,7 +28,8 @@ class CalculatorApp(App):
         "plus_minus_sign": "plus-minus",
         "percent_sign": "percent",
         "equals_sign": "equals",
-        "enter": "equals",
+        "minus": "minus",
+        "plus": "plus",
     }
 
     def watch_numbers(self, value: str) -> None:
@@ -80,7 +81,6 @@ class CalculatorApp(App):
                 self.query_one(f"#{button_id}", Button).press()
             except NoMatches:
                 pass
-            self.set_focus(None)
 
         key = event.key
         if key.isdecimal():
@@ -89,7 +89,9 @@ class CalculatorApp(App):
             press("c")
             press("ac")
         else:
-            press(self.NAME_MAP.get(key, key))
+            button_id = self.NAME_MAP.get(key)
+            if button_id is not None:
+                press(self.NAME_MAP.get(key, key))
 
     def on_button_pressed(self, event: Button.Pressed) -> None:
         """Called when a button is pressed."""
diff --git a/src/textual/css/query.py b/src/textual/css/query.py
index 93addb6fb..e0d588204 100644
--- a/src/textual/css/query.py
+++ b/src/textual/css/query.py
@@ -20,7 +20,7 @@ from typing import cast, Generic, TYPE_CHECKING, Iterator, TypeVar, overload
 
 import rich.repr
 
-from .errors import DeclarationError
+from .errors import DeclarationError, TokenError
 from .match import match
 from .model import SelectorSet
 from .parse import parse_declarations, parse_selectors
@@ -34,6 +34,10 @@ class QueryError(Exception):
     """Base class for a query related error."""
 
 
+class InvalidQueryFormat(QueryError):
+    """Query did not parse correctly."""
+
+
 class NoMatches(QueryError):
     """No nodes matched the query."""
 
@@ -72,9 +76,17 @@ class DOMQuery(Generic[QueryType]):
             parent._excludes.copy() if parent else []
         )
         if filter is not None:
-            self._filters.append(parse_selectors(filter))
+            try:
+                self._filters.append(parse_selectors(filter))
+            except TokenError:
+                # TODO: More helpful errors
+                raise InvalidQueryFormat(f"Unable to parse filter {filter!r} as query")
+
         if exclude is not None:
-            self._excludes.append(parse_selectors(exclude))
+            try:
+                self._excludes.append(parse_selectors(exclude))
+            except TokenError:
+                raise InvalidQueryFormat(f"Unable to parse filter {filter!r} as query")
 
     @property
     def node(self) -> DOMNode:
diff --git a/tests/test_query.py b/tests/test_query.py
index be6108046..373d8d0ee 100644
--- a/tests/test_query.py
+++ b/tests/test_query.py
@@ -1,4 +1,7 @@
+import pytest
+
 from textual.widget import Widget
+from textual.css.query import InvalidQueryFormat
 
 
 def test_query():
@@ -78,3 +81,16 @@ def test_query():
         assert list(app.query("#widget1, #widget2")) == [widget1, widget2]
         assert list(app.query("#widget1 , #widget2")) == [widget1, widget2]
         assert list(app.query("#widget1, #widget2, App")) == [app, widget1, widget2]
+
+
+def test_invalid_query():
+    class App(Widget):
+        pass
+
+    app = App()
+
+    with pytest.raises(InvalidQueryFormat):
+        app.query("#3")
+
+    with pytest.raises(InvalidQueryFormat):
+        app.query("#foo").exclude("#2")