diff --git a/mod/workshop/form/accumulative/db/upgradelib.php b/mod/workshop/form/accumulative/db/upgradelib.php
index 634811f0965..3376c864067 100644
--- a/mod/workshop/form/accumulative/db/upgradelib.php
+++ b/mod/workshop/form/accumulative/db/upgradelib.php
@@ -73,6 +73,10 @@ function workshopform_accumulative_upgrade_legacy() {
         $rs = $DB->get_recordset_sql($sql, $params);
         $newassessmentids = workshop_upgrade_assessment_id_mappings();
         foreach ($rs as $old) {
+            if (!isset($newassessmentids[$old->assessmentid])) {
+                // orphaned grade - the assessment was removed but the grade remained
+                continue;
+            }
             if (!isset($newelementids[$old->workshopid]) or !isset($newelementids[$old->workshopid][$old->elementno])) {
                 // orphaned grade - the assessment form element has been removed after the grade was recorded
                 continue;
diff --git a/mod/workshop/form/comments/db/upgradelib.php b/mod/workshop/form/comments/db/upgradelib.php
index 1d7d3faa78f..f1e537bb6e1 100644
--- a/mod/workshop/form/comments/db/upgradelib.php
+++ b/mod/workshop/form/comments/db/upgradelib.php
@@ -70,6 +70,10 @@ function workshopform_comments_upgrade_legacy() {
         $rs = $DB->get_recordset_sql($sql, $params);
         $newassessmentids = workshop_upgrade_assessment_id_mappings();
         foreach ($rs as $old) {
+            if (!isset($newassessmentids[$old->assessmentid])) {
+                // orphaned comment - the assessment was removed but the grade remained
+                continue;
+            }
             if (!isset($newelementids[$old->workshopid]) or !isset($newelementids[$old->workshopid][$old->elementno])) {
                 // orphaned comment - the assessment form element has been removed after the grade was recorded
                 continue;
diff --git a/mod/workshop/form/numerrors/db/upgradelib.php b/mod/workshop/form/numerrors/db/upgradelib.php
index cf169186442..f7b07f86ddb 100644
--- a/mod/workshop/form/numerrors/db/upgradelib.php
+++ b/mod/workshop/form/numerrors/db/upgradelib.php
@@ -93,6 +93,10 @@ function workshopform_numerrors_upgrade_legacy() {
         $rs = $DB->get_recordset_sql($sql, $params);
         $newassessmentids = workshop_upgrade_assessment_id_mappings();
         foreach ($rs as $old) {
+            if (!isset($newassessmentids[$old->assessmentid])) {
+                // orphaned grade - the assessment was removed but the grade remained
+                continue;
+            }
             if (!isset($newelementids[$old->workshopid]) or !isset($newelementids[$old->workshopid][$old->elementno])) {
                 // orphaned grade - the assessment form element has been removed after the grade was recorded
                 continue;
diff --git a/mod/workshop/form/rubric/db/upgradelib.php b/mod/workshop/form/rubric/db/upgradelib.php
index 34ec718231d..40df767619e 100644
--- a/mod/workshop/form/rubric/db/upgradelib.php
+++ b/mod/workshop/form/rubric/db/upgradelib.php
@@ -104,6 +104,10 @@ function workshopform_rubric_upgrade_legacy_criterion() {
         $newassessmentids = workshop_upgrade_assessment_id_mappings();
         $newdimensionids = $DB->get_records('workshopform_rubric_levels', array(), '', 'id,dimensionid');
         foreach ($rs as $old) {
+            if (!isset($newassessmentids[$old->assessmentid])) {
+                // orphaned grade - the assessment was removed but the grade remained
+                continue;
+            }
             if (!isset($newelementids[$old->workshopid]) or !isset($newelementids[$old->workshopid][$old->elementno])) {
                 // orphaned grade - the assessment form element has been removed after the grade was recorded
                 continue;