diff --git a/packages/backend/src/core/DownloadService.ts b/packages/backend/src/core/DownloadService.ts
index 5d0aaa9945..cb5bdb6cb7 100644
--- a/packages/backend/src/core/DownloadService.ts
+++ b/packages/backend/src/core/DownloadService.ts
@@ -101,7 +101,7 @@ export class DownloadService {
 			await stream.pipeline(req, fs.createWriteStream(path));
 		} catch (e) {
 			if (e instanceof Got.HTTPError) {
-				throw new StatusError(`${e.response.statusCode} ${e.response.statusMessage}`, e.response.statusCode, e.response.statusMessage, e);
+				throw new StatusError(`download error from ${url}`, e.response.statusCode, e.response.statusMessage, e);
 			} else if (e instanceof Got.RequestError || e instanceof Got.AbortError) {
 				throw new Error(String(e), { cause: e });
 			} else if (e instanceof Error) {
diff --git a/packages/backend/src/core/HttpRequestService.ts b/packages/backend/src/core/HttpRequestService.ts
index a0f2607ddc..151097095d 100644
--- a/packages/backend/src/core/HttpRequestService.ts
+++ b/packages/backend/src/core/HttpRequestService.ts
@@ -331,7 +331,7 @@ export class HttpRequestService {
 		});
 
 		if (!res.ok && extra.throwErrorWhenResponseNotOk) {
-			throw new StatusError(`${res.status} ${res.statusText}`, res.status, res.statusText);
+			throw new StatusError(`request error from ${url}`, res.status, res.statusText);
 		}
 
 		if (res.ok) {
diff --git a/packages/backend/src/misc/render-inline-error.ts b/packages/backend/src/misc/render-inline-error.ts
index 36de0262ef..9536d5ea0e 100644
--- a/packages/backend/src/misc/render-inline-error.ts
+++ b/packages/backend/src/misc/render-inline-error.ts
@@ -18,6 +18,8 @@ export function renderInlineError(err: unknown): string {
 	if (err instanceof StatusError) {
 		if (err.message) {
 			return `${err.name} ${err.statusCode}: ${err.message}`;
+		} else if (err.statusMessage) {
+			return `${err.name} ${err.statusCode}: ${err.statusMessage}`;
 		} else {
 			return `${err.name} ${err.statusCode}`;
 		}
diff --git a/packages/backend/src/server/FileServerService.ts b/packages/backend/src/server/FileServerService.ts
index e5d8f39e5a..1a372cb789 100644
--- a/packages/backend/src/server/FileServerService.ts
+++ b/packages/backend/src/server/FileServerService.ts
@@ -384,7 +384,7 @@ export class FileServerService {
 			) {
 				if (!isConvertibleImage) {
 					// 画像でないなら404でお茶を濁す
-					throw new StatusError('Unexpected mime', 404);
+					throw new StatusError(`Unexpected non-convertible mime: ${file.mime}`, 404, 'Unexpected mime');
 				}
 			}
 
@@ -448,7 +448,7 @@ export class FileServerService {
 			} else if (file.mime === 'image/svg+xml') {
 				image = this.imageProcessingService.convertToWebpStream(file.path, 2048, 2048);
 			} else if (!file.mime.startsWith('image/') || !FILE_TYPE_BROWSERSAFE.includes(file.mime)) {
-				throw new StatusError('Rejected type', 403, 'Rejected type');
+				throw new StatusError(`Blocked mime type: ${file.mime}`, 403, 'Blocked mime type');
 			}
 
 			if (!image) {
@@ -522,7 +522,7 @@ export class FileServerService {
 	> {
 		if (url.startsWith(`${this.config.url}/files/`)) {
 			const key = url.replace(`${this.config.url}/files/`, '').split('/').shift();
-			if (!key) throw new StatusError('Invalid File Key', 400, 'Invalid File Key');
+			if (!key) throw new StatusError(`Invalid file URL ${url}`, 400, 'Invalid file url');
 
 			return await this.getFileFromKey(key);
 		}