Fix punctuation.
diff --git a/Doc/library/signal.rst b/Doc/library/signal.rst
index a7cf33d..32fd393 100644
--- a/Doc/library/signal.rst
+++ b/Doc/library/signal.rst
@@ -157,7 +157,7 @@
 
    The old values are returned as a tuple: (delay, interval).
 
-   Attempting to pass an invalid interval timer will cause a
+   Attempting to pass an invalid interval timer will cause an
    :exc:`ItimerError`.
 
    .. versionadded:: 2.6