diff --git a/autoload/ale/highlight.vim b/autoload/ale/highlight.vim
index 348226ea..b57931f6 100644
--- a/autoload/ale/highlight.vim
+++ b/autoload/ale/highlight.vim
@@ -63,8 +63,9 @@ function! ale#highlight#SetHighlights(buffer, loclist) abort
         " we next open it.
         "
         " We'll filter the loclist down to items we can set now.
+        let temp_loclist = deepcopy(a:loclist)
         let s:buffer_highlights[a:buffer] = filter(
-        \   a:loclist,
+        \   temp_loclist,
         \   'v:val.bufnr == a:buffer && v:val.col > 0'
         \)