diff --git a/Data/Dates.hs b/Data/Dates.hs
--- a/Data/Dates.hs
+++ b/Data/Dates.hs
@@ -8,7 +8,7 @@
    pDate, pDateTime, pTime,
    pDateInterval,
    getCurrentDateTime,
-   tryRead,
+   tryRead, tryReadInt,
    DateIntervalType (..),
    DateInterval (..),
    dayToDateTime, dateTimeToDay,
@@ -32,6 +32,7 @@
 import Text.Parsec
 import Text.Parsec.String
 import Data.Generics
+import Data.Char (toLower)
 
 import Data.Dates.Types
 import Data.Dates.Internal
@@ -285,7 +286,12 @@
 pDateIntervalType ∷ Parsec String st DateIntervalType
 pDateIntervalType = do
   s ← choice $ map maybePlural ["day", "week", "month", "year"]
-  tryRead s
+  case head s of
+    'd' → return Day
+    'w' → return Week
+    'm' → return Month
+    'y' → return Year
+    _ → fail $ "Unknown date interval type: " ++ s
 
 pDateInterval ∷ Parsec String st DateInterval
 pDateInterval = do
@@ -293,10 +299,10 @@
   spaces
   tp ← pDateIntervalType
   case tp of
-    Day →   Days   `fmap` tryRead n
-    Week →  Weeks  `fmap` tryRead n
-    Month → Months `fmap` tryRead n
-    Year →  Years  `fmap` tryRead n
+    Day →   Days   `fmap` tryReadInt n
+    Week →  Weeks  `fmap` tryReadInt n
+    Month → Months `fmap` tryReadInt n
+    Year →  Years  `fmap` tryReadInt n
 
 pRelDate ∷ DateTime → Parsec String st DateTime
 pRelDate date = do
@@ -354,7 +360,15 @@
 pWeekDay ∷ Parsec String st WeekDay
 pWeekDay = do
   w ← many1 (oneOf "mondaytueswnhrfi")
-  tryRead (capitalize w)
+  case map toLower w of
+    "monday"    → return Monday
+    "tuesday"   → return Tuesday
+    "wednesday" → return Wednesday
+    "thursday"  → return Thursday
+    "friday"    → return Friday
+    "saturday"  → return Saturday
+    "sunday"    → return Sunday
+    _           → fail $ "Unknown weekday: " ++ w
 
 futureDate ∷ Parsec String st DateInterval
 futureDate = do
@@ -363,10 +377,10 @@
   char ' '
   tp ← pDateIntervalType
   case tp of
-    Day →   Days   `fmap` tryRead n
-    Week →  Weeks  `fmap` tryRead n
-    Month → Months `fmap` tryRead n
-    Year →  Years  `fmap` tryRead n
+    Day →   Days   `fmap` tryReadInt n
+    Week →  Weeks  `fmap` tryReadInt n
+    Month → Months `fmap` tryReadInt n
+    Year →  Years  `fmap` tryReadInt n
 
 passDate ∷ Parsec String st DateInterval
 passDate = do
@@ -375,10 +389,10 @@
   tp ← pDateIntervalType
   string " ago"
   case tp of
-    Day →   (Days   . negate) `fmap` tryRead n
-    Week →  (Weeks  . negate) `fmap` tryRead n
-    Month → (Months . negate) `fmap` tryRead n
-    Year →  (Years  . negate) `fmap` tryRead n
+    Day →   (Days   . negate) `fmap` tryReadInt n
+    Week →  (Weeks  . negate) `fmap` tryReadInt n
+    Month → (Months . negate) `fmap` tryReadInt n
+    Year →  (Years  . negate) `fmap` tryReadInt n
 
 today ∷ Parsec String st DateInterval
 today = do
diff --git a/Data/Dates/Internal.hs b/Data/Dates/Internal.hs
--- a/Data/Dates/Internal.hs
+++ b/Data/Dates/Internal.hs
@@ -2,6 +2,8 @@
 
 module Data.Dates.Internal where
 
+import Data.Char
+
 import Text.Parsec
 import Text.Parsec.String
 
@@ -12,6 +14,12 @@
     [(res, "")] -> return res
     _ -> fail $ "Cannot read: " ++ str
 
+tryReadInt ∷ Num a ⇒ String → Parsec String st a
+tryReadInt str =
+  if all isDigit str
+    then return $ fromIntegral $ foldl (\a b → 10*a+b) 0 $ map digitToInt str
+    else fail $ "Cannot read: " ++ str
+
 -- | Apply parser N times
 times ∷ Int
      → Parsec String st t
@@ -30,7 +38,7 @@
        → Int   -- ^ Maximum value
        → Parsec String st Int
 number n m = do
-  t ← tryRead =<< (n `times` digit)
+  t ← tryReadInt =<< (n `times` digit)
   if t > m
     then fail "number too large"
     else return t
diff --git a/dates.cabal b/dates.cabal
--- a/dates.cabal
+++ b/dates.cabal
@@ -1,5 +1,5 @@
 name:                dates
-version:             0.2.1.0
+version:             0.2.1.1
 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.
@@ -40,12 +40,14 @@
                        Data.Dates.Types,
                        Data.Dates.Formats,
                        Data.Dates.Internal
-  -- other-modules:       
+
   build-depends:       base >=4 && < 5,
                        base-unicode-symbols ==0.2.*,
                        time >= 1.4,
-                       parsec ==3.1.*,
+                       parsec >=3.1,
                        syb ==0.3.*
+
+  GHC-Options:         -O2
 
 Source-repository head
   type:     git