diff --git a/main.go b/main.go
index 985ee70..b686d13 100644
--- a/main.go
+++ b/main.go
@@ -307,7 +307,7 @@ func getProtocol(r *http.Request) string {
 func detectContentType(filename string) string {
 	ext := filepath.Ext(filename)
 	mimeType := mime.TypeByExtension(ext)
-	if mimeType == "" {
+	if mimeType != "" {
 		return mimeType
 	}
 	return "application/octet-stream"