Minor grammar refinement for hmac.compare_digest().
diff --git a/Doc/library/hmac.rst b/Doc/library/hmac.rst
index 38f1687..0706ff4 100644
--- a/Doc/library/hmac.rst
+++ b/Doc/library/hmac.rst
@@ -80,8 +80,8 @@
    .. note::
 
       If *a* and *b* are of different lengths, or if an error occurs,
-      a timing attack may be able to reveal information about the types
-      and lengths of *a* and *b*, but not their values.
+      a timing attack could theoretically reveal information about the
+      types and lengths of *a* and *b*--but not their values.
 
 
    .. versionadded:: 3.3