diff --git a/autoload/ale/highlight.vim b/autoload/ale/highlight.vim
index 1669ebd..54103aa 100644
--- a/autoload/ale/highlight.vim
+++ b/autoload/ale/highlight.vim
@@ -22,12 +22,16 @@ function! ale#highlight#UnqueueHighlights(buffer) abort
     endif
 endfunction
 
-function! s:RemoveOldHighlights() abort
+function! s:GetALEMatches() abort
+    let l:list = []
+
     for l:match in getmatches()
         if l:match['group'] ==# 'ALEError' || l:match['group'] ==# 'ALEWarning'
-            call matchdelete(l:match['id'])
+            call add(l:list, l:match)
         endif
     endfor
+
+    return l:list
 endfunction
 
 function! ale#highlight#UpdateHighlights() abort
@@ -36,7 +40,9 @@ function! ale#highlight#UpdateHighlights() abort
     let l:loclist = l:has_new_items ? remove(s:buffer_highlights, l:buffer) : []
 
     if l:has_new_items || !g:ale_enabled
-        call s:RemoveOldHighlights()
+        for l:match in s:GetALEMatches()
+            call matchdelete(l:match['id'])
+        endfor
     endif
 
     if l:has_new_items
@@ -46,7 +52,10 @@ function! ale#highlight#UpdateHighlights() abort
             let l:line = l:item.lnum
             let l:size = 1
 
-            call matchaddpos(l:group, [[l:line, l:col, l:size]])
+            " Rememeber the match ID for the item.
+            " This ID will be used to preserve loclist items which are set
+            " many times.
+            let l:item.match_id = matchaddpos(l:group, [[l:line, l:col, l:size]])
         endfor
     endif
 endfunction
@@ -64,7 +73,7 @@ function! ale#highlight#SetHighlights(buffer, loclist) abort
         "
         " We'll filter the loclist down to items we can set now.
         let s:buffer_highlights[a:buffer] = filter(
-        \   deepcopy(a:loclist),
+        \   copy(a:loclist),
         \   'v:val.bufnr == a:buffer && v:val.col > 0'
         \)
 
diff --git a/autoload/ale/sign.vim b/autoload/ale/sign.vim
index 1a39ba8..fc12e15 100644
--- a/autoload/ale/sign.vim
+++ b/autoload/ale/sign.vim
@@ -125,8 +125,7 @@ function! ale#sign#SetSigns(buffer, loclist) abort
         \   : 'ALEWarningSign'
 
         " Save the sign IDs we are setting back on our loclist objects.
-        " These IDs can be used later for changing line numbers of items
-        " we keep, based on what Vim adjusts automatically.
+        " These IDs will be used to preserve items which are set many times.
         for l:obj in l:sublist
             let l:obj.sign_id = l:sign_id
         endfor
diff --git a/test/test_highlight_placement.vader b/test/test_highlight_placement.vader
index b3e40c1..2bf37d1 100644
--- a/test/test_highlight_placement.vader
+++ b/test/test_highlight_placement.vader
@@ -4,27 +4,18 @@ Before:
     \ {
     \   'lnum': 1,
     \   'col': 1,
-    \   'bufnr': bufnr('%'),
-    \   'vcol': 0,
-    \   'nr': -1,
     \   'type': 'E',
     \   'text': 'foo',
     \ },
     \ {
     \   'lnum': 2,
     \   'col': 1,
-    \   'bufnr': bufnr('%'),
-    \   'vcol': 0,
-    \   'nr': -1,
     \   'type': 'W',
     \   'text': 'bar',
     \ },
     \ {
     \   'lnum': 3,
     \   'col': 5,
-    \   'bufnr': bufnr('%'),
-    \   'vcol': 0,
-    \   'nr': -1,
     \   'type': 'E',
     \   'text': 'wat',
     \ },
@@ -59,3 +50,5 @@ Execute(Highlights should be set when a linter runs):
   \   {'group': 'ALEError', 'id': 6, 'priority': 10, 'pos1': [3, 5, 1]}
   \ ],
   \ getmatches()
+
+  AssertEqual [4, 5, 6], map(copy(g:ale_buffer_info[bufnr('')].loclist), 'v:val.match_id')
diff --git a/test/test_linting_updates_loclist.vader b/test/test_linting_updates_loclist.vader
index 2e106d0..a73a504 100644
--- a/test/test_linting_updates_loclist.vader
+++ b/test/test_linting_updates_loclist.vader
@@ -36,4 +36,8 @@ Execute(The loclist should be updated after linting is done):
   call ale#engine#WaitForJobs(2000)
 
   AssertEqual ['' . bufnr('%')], keys(g:ale_buffer_info)
+
+  let g:expected_data[0].match_id = getmatches()[0].id
+  let g:expected_data[1].match_id = getmatches()[1].id
+
   AssertEqual g:expected_data, g:ale_buffer_info[bufnr('%')].loclist