diff --git a/src/routes/postClearCache.ts b/src/routes/postClearCache.ts
index 29979c09..e446c4b7 100644
--- a/src/routes/postClearCache.ts
+++ b/src/routes/postClearCache.ts
@@ -23,7 +23,7 @@ export async function postClearCache(req: Request, res: Response): Promise<Respo
 
     if (invalidFields.length !== 0) {
         // invalid request
-        const fields = invalidFields.reduce((p, c, i) => p + (i !== 0 ? ", " : "") + c, "");
+        const fields = invalidFields.join(", ");
         return res.status(400).send(`No valid ${fields} field(s) provided`);
     }
 
diff --git a/src/routes/postSkipSegments.ts b/src/routes/postSkipSegments.ts
index 217be5c9..70ddbd83 100644
--- a/src/routes/postSkipSegments.ts
+++ b/src/routes/postSkipSegments.ts
@@ -242,8 +242,8 @@ async function checkInvalidFields(videoID: VideoID, userID: UserID, hashedUserID
 
     if (invalidFields.length !== 0) {
         // invalid request
-        const formattedFields = invalidFields.reduce((p, c, i) => p + (i !== 0 ? ", " : "") + c, "");
-        const formattedErrors = errors.reduce((p, c, i) => p + (i !== 0 ? ". " : " ") + c, "");
+        const formattedFields = invalidFields.join(", ");
+        const formattedErrors = errors.join(". ");
         return {
             pass: false,
             errorMessage: `No valid ${formattedFields}.${formattedErrors}`,