diff --git a/packages/backend/src/server/ServerUtilityService.ts b/packages/backend/src/server/ServerUtilityService.ts
index 115717534f..8cecc5df58 100644
--- a/packages/backend/src/server/ServerUtilityService.ts
+++ b/packages/backend/src/server/ServerUtilityService.ts
@@ -37,9 +37,13 @@ export class ServerUtilityService {
 				for await (const part of request.parts()) {
 					if (part.type === 'field') {
 						const k = part.fieldname;
-						const v = String(part.value);
+						const v = part.value;
 						const body = request.body ??= {};
 
+						// Value can be string, buffer, or undefined.
+						// We only support the first one.
+						if (typeof(v) !== 'string') continue;
+
 						// This is just progressive conversion from undefined -> string -> string[]
 						if (body[k]) {
 							if (Array.isArray(body[k])) {