diff --git a/dist/index.js b/dist/index.js
index 0f2d3a2..a8c87fc 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -19269,7 +19269,7 @@ function run() {
         if (applicableChecklistPaths.length > 0) {
             const body = [
                 `${header}\n\n`,
-                ...applicableChecklistPaths.map(([path, items]) => formatItemsForPath(existingComment.body, [path, items])),
+                ...applicableChecklistPaths.map(([path, items]) => formatItemsForPath(!!existingComment ? existingComment.body : undefined, [path, items])),
                 `\n${footer}`,
             ].join("");
             if (existingComment) {
diff --git a/index.ts b/index.ts
index 78df1e8..4b881ed 100644
--- a/index.ts
+++ b/index.ts
@@ -103,7 +103,10 @@ async function run() {
     const body = [
       `${header}\n\n`,
       ...applicableChecklistPaths.map(([path, items]) =>
-        formatItemsForPath(existingComment.body, [path, items])
+        formatItemsForPath(
+          !!existingComment ? existingComment.body : undefined,
+          [path, items]
+        )
       ),
       `\n${footer}`,
     ].join("");