diff --git a/src/app/workflow-spec-list/workflow-spec-list.component.ts b/src/app/workflow-spec-list/workflow-spec-list.component.ts
index 23ea5c7..45cf082 100644
--- a/src/app/workflow-spec-list/workflow-spec-list.component.ts
+++ b/src/app/workflow-spec-list/workflow-spec-list.component.ts
@@ -221,7 +221,7 @@ export class WorkflowSpecListComponent implements OnInit {
   editCategoryDisplayOrder(catId: number, direction: string) {
     this.api.reorderWorkflowCategory(catId, direction).subscribe(cat_change => {
         this.workflowSpecsByCategory = this.workflowSpecsByCategory.map(cat => {
-          let new_cat = cat_change.find(i2 => i2.id === cat.id);
+          let new_cat = this.ensure(cat_change.find(i2 => i2.id === cat.id));
           cat.display_order = new_cat.display_order;
           return cat;
         });
@@ -229,6 +229,15 @@ export class WorkflowSpecListComponent implements OnInit {
     });
   }
 
+  // ensure that in array.find, we find what we are expecting. (Ensures TS type safety)
+  ensure<T>(argument: T | undefined | null, message: string = 'Spec not found!'): T {
+    if (argument === undefined || argument === null) {
+      throw new TypeError(message);
+    }
+    return argument;
+  }
+
+
   editSpecDisplayOrder(cat: WorkflowSpecCategoryGroup, specId: string, direction: string) {
     this.api.reorderWorkflowSpecification(specId, direction).subscribe(wfs => {
       cat.workflow_specs= wfs;