diff --git a/node_modules/catalog.js b/node_modules/catalog.js
index abe440b..a859e0f 100644
--- a/node_modules/catalog.js
+++ b/node_modules/catalog.js
@@ -77,17 +77,19 @@ Catalog.prototype.update = function(code) {
 			}
 
 			var newcrns = [];
-			for (var type in course.sections) {
-				course.sections[type].forEach((section) => {
-					var idx = oldcrns.indexOf(section.crn);
-					if (idx == -1) {
-						newcrns.push(section.crn);
-					} else {
-						oldcrns.splice(idx, 1);
-					}
-					this.sections[section.crn] = section;
-					section.course = course;
-				});
+			if (oldcrns.length != 0) {
+				for (var type in course.sections) {
+					course.sections[type].forEach((section) => {
+						var idx = oldcrns.indexOf(section.crn);
+						if (idx == -1) {
+							newcrns.push(section.crn);
+						} else {
+							oldcrns.splice(idx, 1);
+						}
+						this.sections[section.crn] = section;
+						section.course = course;
+					});
+				}
 			}
 			resolve({course: course, added: newcrns, removed: oldcrns});
 		}).bind(this), (err) => {