diff --git a/src/routes/(app)/+page.svelte b/src/routes/(app)/+page.svelte
index 108340e..5a30e66 100644
--- a/src/routes/(app)/+page.svelte
+++ b/src/routes/(app)/+page.svelte
@@ -40,7 +40,7 @@
 					<Link href="survey/{survey.id}">{survey.title}</Link>
 					<span class="mr-5 inline-block">
 						({survey.fillRate.filled}/{survey.fillRate.expected})
-						{#if survey.fillRate.filled === survey.fillRate.expected}
+						{#if survey.fillRate.filled === survey.fillRate.expected && survey.fillRate.expected > 0}
 							<CheckIcon />
 						{/if}
 					</span>
diff --git a/src/routes/(app)/survey/[surveyId]/+page.svelte b/src/routes/(app)/survey/[surveyId]/+page.svelte
index 91cc3fb..ae024e0 100644
--- a/src/routes/(app)/survey/[surveyId]/+page.svelte
+++ b/src/routes/(app)/survey/[surveyId]/+page.svelte
@@ -17,13 +17,22 @@
 
 	let { data }: { data: PageData } = $props();
 
-	const diagramData = data.skills.flatMap((skill) =>
-		data.participants.map((participant) => ({
-			skill: skill.title,
-			participant: participant.id,
-			rating: participant.answers.find((answer) => answer.skillId === skill.id)?.rating
-		}))
-	);
+	const diagramData = data.skills.flatMap((skill) => {
+		if (data.participants.length > 0) {
+			return data.participants.map((participant) => ({
+				skill: skill.title,
+				participant: participant.id,
+				rating: participant.answers.find((answer) => answer.skillId === skill.id)?.rating
+			}));
+		} else {
+			// fallback pseudo participant because empty diagram data will break the diagram and make the survey page unaccessible
+			return {
+				skill: skill.title,
+				participant: -1,
+				rating: undefined
+			};
+		}
+	});
 
 	function copyLinkToClipboard(link: string) {
 		navigator.clipboard.writeText(link);
diff --git a/src/routes/(app)/survey/[surveyId]/edit/+page.server.ts b/src/routes/(app)/survey/[surveyId]/edit/+page.server.ts
index 0e20af7..4883557 100644
--- a/src/routes/(app)/survey/[surveyId]/edit/+page.server.ts
+++ b/src/routes/(app)/survey/[surveyId]/edit/+page.server.ts
@@ -5,7 +5,7 @@ import debug from 'debug';
 import { fromFormData } from '$lib/survey';
 import { db } from '../../../../../db';
 import { surveyAccessTable, surveyAnswersTable, surveySkillsTable, surveysTable } from '../../../../../db/schema';
-import { eq, inArray } from 'drizzle-orm';
+import { eq, inArray, and } from 'drizzle-orm';
 import { addParticipant, addSkill, loadSurveyData } from '../../../../../db/survey';
 
 const log = debug('survey:admin:edit');
@@ -58,10 +58,13 @@ export const actions = {
         // update the participants where applicable (unchanged participants are left untouched)
         const deletedParticipants = survey.participants.filter(participant => !participants.includes(participant.email));
         const newParticipants = participants.filter(email => !survey.participants.some(candidate => candidate.email === email));
-        // delete all participants no longer part of the survey
-        await db.delete(surveyAccessTable).where(inArray(surveyAccessTable.recepientEmail, deletedParticipants.map(participant => participant.email)));
-        // delete answers from deleted participants
-        await db.delete(surveyAnswersTable).where(inArray(surveyAnswersTable.participantId, deletedParticipants.map(participant => participant.id)));
+        // delete all participants no longer part of the survey (this should also delete their answers via cascade delete)
+        await db.delete(surveyAccessTable).where(
+            and(
+                eq(surveyAccessTable.surveyId, survey.id),
+                inArray(surveyAccessTable.recepientEmail, deletedParticipants.map(participant => participant.email))
+            )
+        );
         // add any new participants
         for (const newParticipant of newParticipants) {
             await addParticipant(survey.id, newParticipant);