diff --git a/templates/lecture.html b/templates/lecture.html
index e3b8eb637324b0cfb3a5a67ee3de66cecb756e8d..ab2a96a950d15c7fd8bda759a9a547ac9f038ceb 100644
--- a/templates/lecture.html
+++ b/templates/lecture.html
@@ -128,7 +128,7 @@ $(function() {
 					var m = zeropad( Math.trunc((timestamp%3600)/60),2);
 					var s = zeropad( Math.trunc(timestamp%60),2);
 					var timeasstring = h+':'+m+':'+s;
-					return '<form method="post" data-url="{{ url_for('suggest_chapter', lectureid=lecture.id) }}" onSubmit="return hintchapterclick(this);"><input class="form-control" placeholder="00:00.000" name="time" type="text" value="'+timeasstring+'"><br><input class="form-control" placeholder="Kapitel" name="text" type="text"><br><input type="submit" class="btn btn-default" value="{% if ismod() %}Hinzufügen{% else %}Vorschlagen{% endif %}"></form>';
+					return '<form class="needs-validation" method="post" data-url="{{ url_for('suggest_chapter', lectureid=lecture.id) }}" onSubmit="return hintchapterclick(this);"><input class="form-control" placeholder="00:00" name="time" type="text" value="'+timeasstring+'" pattern="(|[0-9]{1,2}:(|[0-9]{1,2}:))[0-9]{1,2}"><br><input class="form-control" placeholder="Titel" name="text" type="text" required><br><input type="submit" class="btn btn-default" value="{% if ismod() %}Hinzufügen{% else %}Vorschlagen{% endif %}"></form>';
 				}
 			})