diff --git a/packages/backend/src/core/FileInfoService.ts b/packages/backend/src/core/FileInfoService.ts
index e7d106a285..fab2af658c 100644
--- a/packages/backend/src/core/FileInfoService.ts
+++ b/packages/backend/src/core/FileInfoService.ts
@@ -341,16 +341,15 @@ export class FileInfoService {
 	}
 
 	/**
-	 * Detect MIME Type and extension by stream for performance (this cannot detect SVG)
+	 * Detect MIME Type and extension by stream and path for performance
 	 */
 	@bindThis
-	public async detectRequestType(_response: Response): Promise<{
+	public async detectRequestType(_response: Response, path?: string, fileSavingPromise: Promise<any> = Promise.resolve()): Promise<{
 		mime: string;
 		ext: string | null;
 	}> {
 		const response = _response.clone();
 
-		// Check 0 byte
 		if (!response.body) {
 			throw new StatusError('No Body', 400, 'No Body');
 		}
@@ -358,12 +357,26 @@ export class FileInfoService {
 		const type = await fileTypeFromStream(stream.Readable.fromWeb(response.body));
 
 		if (type) {
+			// XMLはSVGかもしれない
+			if (path && type.mime === 'application/xml') {
+				await fileSavingPromise;
+				if (await this.checkSvg(path)) {
+					return TYPE_SVG;
+				}	
+			}
+
 			return {
 				mime: type.mime,
 				ext: type.ext,
 			};
 		}
 
+		// 種類が不明でもSVGかもしれない
+		if (path) {
+			await fileSavingPromise;
+			if (await this.checkSvg(path)) return TYPE_SVG;
+		}
+
 		// 種類が不明なら application/octet-stream にする
 		return TYPE_OCTET_STREAM;
 	}
diff --git a/packages/backend/src/server/FileServerService.ts b/packages/backend/src/server/FileServerService.ts
index 04ff7113d8..c87041cabf 100644
--- a/packages/backend/src/server/FileServerService.ts
+++ b/packages/backend/src/server/FileServerService.ts
@@ -111,14 +111,7 @@ export class FileServerService {
 					const response = await this.downloadService.fetchUrl(file.uri);
 					const fileSaving = this.downloadService.pipeRequestToFile(response, path);
 
-					let { mime, ext } = await this.fileInfoService.detectRequestType(response);
-					if (mime === 'application/octet-stream' || mime === 'application/xml') {
-						await fileSaving;
-						if (await this.fileInfoService.checkSvg(path)) {
-							mime = TYPE_SVG.mime;
-							ext = TYPE_SVG.ext;
-						}
-					}
+					const { mime, ext } = await this.fileInfoService.detectRequestType(response, path, fileSaving);
 
 					const convertFile = async () => {
 						if (isThumbnail) {
diff --git a/packages/backend/src/server/MediaProxyServerService.ts b/packages/backend/src/server/MediaProxyServerService.ts
index c7def0a386..509ad661c4 100644
--- a/packages/backend/src/server/MediaProxyServerService.ts
+++ b/packages/backend/src/server/MediaProxyServerService.ts
@@ -77,14 +77,7 @@ export class MediaProxyServerService {
 			const response = await this.downloadService.fetchUrl(url);
 			const fileSaving = this.downloadService.pipeRequestToFile(response, path);
 
-			let { mime, ext } = await this.fileInfoService.detectRequestType(response);
-			if (mime === 'application/octet-stream' || mime === 'application/xml') {
-				await fileSaving;
-				if (await this.fileInfoService.checkSvg(path)) {
-					mime = TYPE_SVG.mime;
-					ext = TYPE_SVG.ext;
-				}
-			}
+			const { mime, ext } = await this.fileInfoService.detectRequestType(response, path, fileSaving);
 			const isConvertibleImage = isMimeImage(mime, 'sharp-convertible-image');
 			const isAnimationConvertibleImage = isMimeImage(mime, 'sharp-animation-convertible-image');