diff --git a/Data/Dates.hs b/Data/Dates.hs
--- a/Data/Dates.hs
+++ b/Data/Dates.hs
@@ -286,7 +286,7 @@
 pDateIntervalType ∷ Parsec String st DateIntervalType
 pDateIntervalType = do
   s ← choice $ map maybePlural ["day", "week", "month", "year"]
-  case head s of
+  case toLower (head s) of
     'd' → return Day
     'w' → return Week
     'm' → return Month
diff --git a/dates.cabal b/dates.cabal
--- a/dates.cabal
+++ b/dates.cabal
@@ -1,5 +1,5 @@
 name:                dates
-version:             0.2.1.1
+version:             0.2.1.2
 synopsis:            Small library for parsing different dates formats.
 description:         This package allows to parse many different formats
                      of dates. Both absolute and relative dates are supported.