diff --git a/src/InvidiousAPI.ts b/src/InvidiousAPI.ts
index 074f3bb..70ea031 100644
--- a/src/InvidiousAPI.ts
+++ b/src/InvidiousAPI.ts
@@ -32,7 +32,7 @@ export const getInvidiousSearchURL = (query: string): string =>
   `${INVIDIOUS_API_ENDPOINT}/search?q=${encodeURIComponent(query)}`;
 
 export const getInvidiousThumbnailURL = (url: string): string =>
-  `${INVIDIOUS_BASE_URL}${url}`;
+  `${INVIDIOUS_BASE_URL}/${url}`;
 
 const preferredThumbnailAPIURL = (thumbnails: InvidiousVideoThumbnail[] | undefined): string => {
   if (!thumbnails || thumbnails.length === 0) {
diff --git a/src/server.ts b/src/server.ts
index 3e852ef..0163faa 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -118,7 +118,8 @@ apiRouter.get("/thumbnail", withErrorHandling(async (req, res) => {
     }
 
     try {
-        const response = await fetch(getInvidiousThumbnailURL(thumbnailUrl));
+        const thumbnailUrlWithoutLeadingSlash = thumbnailUrl.startsWith('/') ? thumbnailUrl.slice(1) : thumbnailUrl;
+        const response = await fetch(getInvidiousThumbnailURL(thumbnailUrlWithoutLeadingSlash));
         if (!response.ok) {
             throw new Error(`HTTP error! status: ${response.status}`);
         }