Index: lams_central/web/includes/javascript/addLesson.js
===================================================================
diff -u -r23096623cbfaccffc0b32c9090ab463539a173c8 -rdf453715948c96fbc106a66429e2dd53089a5bd8
--- lams_central/web/includes/javascript/addLesson.js	(.../addLesson.js)	(revision 23096623cbfaccffc0b32c9090ab463539a173c8)
+++ lams_central/web/includes/javascript/addLesson.js	(.../addLesson.js)	(revision df453715948c96fbc106a66429e2dd53089a5bd8)
@@ -735,7 +735,7 @@
 		var maxLearnerCount = $('#selected-learners div.draggableItem').length,
 			learnerCount = $('#splitLearnersCountField').val(),
 			instances = Math.ceil(maxLearnerCount/learnerCount);
-		learnerCount = Math.ceil(maxLearnerCount/instances);
+		learnerCount = instances ? Math.ceil(maxLearnerCount/instances) : learnerCount;
 		var description = SPLIT_LEARNERS_DESCRIPTION.replace('[0]', instances).replace('[1]', learnerCount);
 		$('#splitLearnersDescription').html(description);
 	}