diff --git a/P4/src/twitter/Extract.java b/P4/src/twitter/Extract.java
index c3e0993..6e1af4d 100644
--- a/P4/src/twitter/Extract.java
+++ b/P4/src/twitter/Extract.java
@@ -36,7 +36,7 @@ public static Timespan getTimespan(List<Tweet> tweets) {
      *         A username-mention is "@" followed by a Twitter username (as
      *         defined by Tweet.getAuthor()'s spec).
      *         The username-mention cannot be immediately preceded or followed by any
-     *         character valid in a Twitter username.
+     *         character invalid in a Twitter username.
      *         For this reason, an email address like bitdiddle@mit.edu does NOT 
      *         contain a mention of the username mit.
      *         Twitter usernames are case-insensitive, and the returned set may