Index: wp-content/themes/twentyeleven/style.css
===================================================================
--- wp-content/themes/twentyeleven/style.css	(revision 21466)
+++ wp-content/themes/twentyeleven/style.css	(working copy)
@@ -1960,6 +1960,12 @@
 }
 .commentlist .children li.comment .comment-content {
 	margin: 1.625em 0 0;
+	-ms-word-break: break-all;
+  word-break: break-all;
+	word-break: break-word;
+	-webkit-hyphens: auto;
+	-moz-hyphens: auto;
+	hyphens: auto;
 }
 .comment-meta a {
 	font-weight: bold;