Fix typo -- missing "not" (GH-5528)
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 256bf02..96475b9 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -514,7 +514,7 @@
Rotate the deque *n* steps to the right. If *n* is negative, rotate
to the left.
- When the deque is empty, rotating one step to the right is equivalent
+ When the deque is not empty, rotating one step to the right is equivalent
to ``d.appendleft(d.pop())``, and rotating one step to the left is
equivalent to ``d.append(d.popleft())``.