diff --git a/sqlparse/sql.py b/sqlparse/sql.py
index 5489f055..dabd88bd 100644
--- a/sqlparse/sql.py
+++ b/sqlparse/sql.py
@@ -638,7 +638,7 @@ def get_parameters(self):
     def get_window(self):
         """Return the window if it exists."""
         over_clause = self.token_next_by(i=Over)
-        if not over_clause:
+        if over_clause[1] is None:
             return None
         return over_clause[1].tokens[-1]
 
diff --git a/tests/test_grouping.py b/tests/test_grouping.py
index bf278817..0caaf9a0 100644
--- a/tests/test_grouping.py
+++ b/tests/test_grouping.py
@@ -393,6 +393,10 @@ def test_grouping_function():
     assert isinstance(p.tokens[0], sql.Function)
     assert len(list(p.tokens[0].get_parameters())) == 1
     assert isinstance(p.tokens[0].get_window(), sql.Parenthesis)
+    # A function without an OVER clause has no window.
+    p = sqlparse.parse('foo(5)')[0]
+    assert isinstance(p.tokens[0], sql.Function)
+    assert p.tokens[0].get_window() is None
 
 
 def test_grouping_function_not_in():