diff --git a/.changeset/wicked-zebras-begin.md b/.changeset/wicked-zebras-begin.md
new file mode 100644
index 00000000000..2484e449cc7
--- /dev/null
+++ b/.changeset/wicked-zebras-begin.md
@@ -0,0 +1,5 @@
+---
+"electron-updater": patch
+---
+
+Fixed missing lowercase in extension comparison.
diff --git a/packages/electron-updater/src/AppUpdater.ts b/packages/electron-updater/src/AppUpdater.ts
index 3e7ff8a9e0b..c0ea270c810 100644
--- a/packages/electron-updater/src/AppUpdater.ts
+++ b/packages/electron-updater/src/AppUpdater.ts
@@ -698,7 +698,7 @@ export abstract class AppUpdater extends (EventEmitter as new () => TypedEmitter
     function getCacheUpdateFileName(): string {
       // NodeJS URL doesn't decode automatically
       const urlPath = decodeURIComponent(taskOptions.fileInfo.url.pathname)
-      if (urlPath.endsWith(`.${taskOptions.fileExtension}`)) {
+      if (urlPath.toLowerCase().endsWith(`.${taskOptions.fileExtension.toLowerCase()}`)) {
         return path.basename(urlPath)
       } else {
         // url like /latest, generate name
diff --git a/packages/electron-updater/src/providers/Provider.ts b/packages/electron-updater/src/providers/Provider.ts
index 218f04548fc..dd723da6495 100644
--- a/packages/electron-updater/src/providers/Provider.ts
+++ b/packages/electron-updater/src/providers/Provider.ts
@@ -85,13 +85,13 @@ export function findFile(files: Array<ResolvedUpdateFileInfo>, extension: string
     throw newError("No files provided", "ERR_UPDATER_NO_FILES_PROVIDED")
   }
 
-  const result = files.find(it => it.url.pathname.toLowerCase().endsWith(`.${extension}`))
+  const result = files.find(it => it.url.pathname.toLowerCase().endsWith(`.${extension.toLowerCase()}`))
   if (result != null) {
     return result
   } else if (not == null) {
     return files[0]
   } else {
-    return files.find(fileInfo => !not.some(ext => fileInfo.url.pathname.toLowerCase().endsWith(`.${ext}`)))
+    return files.find(fileInfo => !not.some(ext => fileInfo.url.pathname.toLowerCase().endsWith(`.${ext.toLowerCase()}`)))
   }
 }