diff --git a/src/Animation.jl b/src/Animation.jl
index 790c8b8..923f8df 100644
--- a/src/Animation.jl
+++ b/src/Animation.jl
@@ -125,7 +125,7 @@ function sort_bundle_paths(bundle_paths::Vector{String})
 
     for i in 1:n_bundles
         bundle_path = bundle_paths[i]
-        bundle_num_string = bundle_path[(findfirst("bundle_", s).stop + 1):(end - extension_length)]
+        bundle_num_string = bundle_path[(findfirst("bundle_", bundle_path).stop + 1):(end - extension_length)]
         bundle_nums[i] = parse(Int64, bundle_num_string)
     end