diff --git a/autoload/ale/completion.vim b/autoload/ale/completion.vim
index c14dcd1..9792fc5 100644
--- a/autoload/ale/completion.vim
+++ b/autoload/ale/completion.vim
@@ -49,25 +49,32 @@ function! ale#completion#OmniFunc(findstart, base) abort
 
         return l:column - len(l:match) - 1
     else
-        " Reset the settings now
-        let &omnifunc = b:ale_old_omnifunc
-        let &completeopt = b:ale_old_completeopt
-        let l:response = b:ale_completion_response
-        let l:parser = b:ale_completion_parser
+        " Parse a new response if there is one.
+        if exists('b:ale_completion_response')
+        \&& exists('b:ale_completion_parser')
+            let l:response = b:ale_completion_response
+            let l:parser = b:ale_completion_parser
 
-        unlet b:ale_completion_response
-        unlet b:ale_completion_parser
-        unlet b:ale_old_omnifunc
-        unlet b:ale_old_completeopt
+            unlet b:ale_completion_response
+            unlet b:ale_completion_parser
 
-        return function(l:parser)(l:response)
+            let b:ale_completion_result = function(l:parser)(l:response)
+        endif
+
+        return get(b:, 'ale_completion_result', [])
     endif
 endfunction
 
 function! ale#completion#Show(response, completion_parser) abort
-    " Remember the old omnifunc value.
-    if !exists('b:ale_old_omnifunc')
+    " Remember the old omnifunc value, if there is one.
+    " If we don't store an old one, we'll just never reset the option.
+    " This will stop some random exceptions from appearing.
+    if !exists('b:ale_old_omnifunc') && !empty(&omnifunc)
         let b:ale_old_omnifunc = &omnifunc
+    endif
+
+    " Remember the old completion options, if they are set.
+    if !exists('b:ale_old_completeopt') && !empty(&completeopt)
         let b:ale_old_completeopt = &completeopt
     endif
 
@@ -248,6 +255,12 @@ endfunction
 function! ale#completion#Queue() abort
     let s:timer_pos = getcurpos()[1:2]
 
+    " If we changed the text again while we're still waiting for a response,
+    " then invalidate the requests before the timer ticks again.
+    if exists('b:ale_completion_info')
+        let b:ale_completion_info.request_id = 0
+    endif
+
     if s:timer_id != -1
         call timer_stop(s:timer_id)
     endif
@@ -255,13 +268,28 @@ function! ale#completion#Queue() abort
     let s:timer_id = timer_start(g:ale_completion_delay, function('s:TimerHandler'))
 endfunction
 
+function! ale#completion#Done() abort
+    silent! pclose
+
+    " Reset settings when completion is done.
+    if exists('b:ale_old_omnifunc')
+        let &omnifunc = b:ale_old_omnifunc
+        unlet b:ale_old_omnifunc
+    endif
+
+    if exists('b:ale_old_completeopt')
+        let &completeopt = b:ale_old_completeopt
+        unlet b:ale_old_completeopt
+    endif
+endfunction
+
 function! s:Setup(enabled) abort
     augroup ALECompletionGroup
         autocmd!
 
         if a:enabled
             autocmd TextChangedI * call ale#completion#Queue()
-            autocmd CompleteDone * silent! pclose
+            autocmd CompleteDone * call ale#completion#Done()
         endif
     augroup END