diff --git a/autoload/vimwiki/diary.vim b/autoload/vimwiki/diary.vim
index a229475..43cde5b 100644
--- a/autoload/vimwiki/diary.vim
+++ b/autoload/vimwiki/diary.vim
@@ -58,28 +58,28 @@ function! vimwiki#diary#diary_date_link(...) abort
 
   let l:frequency = vimwiki#vars#get_wikilocal('diary_frequency')
 
-  if l:frequency == "weekly"
+  if l:frequency ==? 'weekly'
     let l:start_week_day = vimwiki#vars#get_wikilocal('diary_start_week_day')
-    let l:weekday_num = str2nr(strftime("%w", l:timestamp))
+    let l:weekday_num = str2nr(strftime('%w', l:timestamp))
     let l:days_to_end_of_week = (7-l:weekday_number[l:start_week_day]+weekday_num) % 7
     let l:computed_timestamp = l:timestamp
           \ + 7*l:day_s*l:delta_periods
           \ - l:day_s*l:days_to_end_of_week
 
-  elseif l:frequency == "monthly"
-    let l:day_of_month = str2nr(strftime("%d", l:timestamp))
+  elseif l:frequency ==? 'monthly'
+    let l:day_of_month = str2nr(strftime('%d', l:timestamp))
     let l:beginning_of_month = l:timestamp - (l:day_of_month - 1)*l:day_s
     let l:middle_of_month = l:beginning_of_month + 15*l:day_s
     let l:middle_of_computed_month = l:middle_of_month + float2nr(30.5*l:day_s*l:delta_periods)
-    let l:day_of_computed_month = str2nr(strftime("%d", l:middle_of_computed_month)) - 1
+    let l:day_of_computed_month = str2nr(strftime('%d', l:middle_of_computed_month)) - 1
     let l:computed_timestamp = l:middle_of_computed_month - l:day_of_computed_month*l:day_s
 
-  elseif l:frequency == "yearly"
-    let l:day_of_year = str2nr(strftime("%j", l:timestamp))
+  elseif l:frequency ==? 'yearly'
+    let l:day_of_year = str2nr(strftime('%j', l:timestamp))
     let l:beginning_of_year = l:timestamp - (l:day_of_year - 1)*l:day_s
     let l:middle_of_year = l:beginning_of_year + float2nr(365.25/2*l:day_s)
     let l:middle_of_computed_year = l:middle_of_year + float2nr(365.25*l:day_s*l:delta_periods)
-    let l:day_of_computed_year = str2nr(strftime("%j", l:middle_of_computed_year)) - 1
+    let l:day_of_computed_year = str2nr(strftime('%j', l:middle_of_computed_year)) - 1
     let l:computed_timestamp = l:middle_of_computed_year - l:day_of_computed_year*l:day_s
 
   else "daily