diff --git a/src/SelectionModel.ts b/src/SelectionModel.ts
index 1fbf40fe..5982b1e9 100644
--- a/src/SelectionModel.ts
+++ b/src/SelectionModel.ts
@@ -97,6 +97,9 @@ export class SelectionModel {
   public areSelectionValuesReversed(): boolean {
     const start = this.selectionStart;
     const end = this.selectionEnd;
+    if (!start || !end) {
+      return false;
+    }
     return start[1] > end[1] || (start[1] === end[1] && start[0] > end[0]);
   }