diff --git a/src/courseware/course/sidebar/sidebars/course-outline/hooks.js b/src/courseware/course/sidebar/sidebars/course-outline/hooks.js
index 71ed4bff63..1bdb115e0d 100644
--- a/src/courseware/course/sidebar/sidebars/course-outline/hooks.js
+++ b/src/courseware/course/sidebar/sidebars/course-outline/hooks.js
@@ -74,9 +74,17 @@ export const useCourseOutlineSidebar = () => {
 
   const handleUnitClick = ({ sequenceId, activeUnitId, id }) => {
     const logEvent = (eventName, widgetPlacement) => {
-      const findSequenceByUnitId = () => Object.values(sequences).find(seq => seq.unitIds.includes(activeUnitId));
+      const findSequenceByUnitId = (searchUnitId) => {
+        if (!searchUnitId) {
+          return null;
+        }
+        return Object.values(sequences).find(seq => seq.unitIds.includes(searchUnitId));
+      };
       const activeSequence = findSequenceByUnitId(activeUnitId);
       const targetSequence = findSequenceByUnitId(id);
+      if (!activeSequence || !targetSequence) {
+        return;
+      }
       const payload = {
         id: activeUnitId,
         current_tab: activeSequence.unitIds.indexOf(activeUnitId) + 1,
@@ -95,7 +103,9 @@ export const useCourseOutlineSidebar = () => {
     };
 
     logEvent('edx.ui.lms.sequence.tab_selected', 'left');
-    dispatch(checkBlockCompletion(courseId, sequenceId, activeUnitId));
+    if (activeUnitId) {
+      dispatch(checkBlockCompletion(courseId, sequenceId, activeUnitId));
+    }
 
     // Hide the sidebar after selecting a unit on a mobile device.
     if (shouldDisplayFullScreen) {
diff --git a/src/courseware/data/thunks.js b/src/courseware/data/thunks.js
index 15d36f7251..2bb76e4a9e 100644
--- a/src/courseware/data/thunks.js
+++ b/src/courseware/data/thunks.js
@@ -176,6 +176,10 @@ export function fetchSequence(sequenceId, isPreview) {
 
 export function checkBlockCompletion(courseId, sequenceId, unitId) {
   return async (dispatch, getState) => {
+    if (!unitId) {
+      return {};
+    }
+
     const { models } = getState();
     if (models.units[unitId]?.complete) {
       return {}; // do nothing. Things don't get uncompleted after they are completed.