diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -15,6 +15,7 @@
 import Data.Ord
 import Statistics.Math.RootFinding
 import Data.Decimal
+import qualified Data.Text as T
 
 
 import Paths_hledger_irr ( version )
@@ -26,8 +27,8 @@
   , optInput        :: FilePath
   , optInvAcc       :: String
   , optInterestAcc  :: String
-  , optBegin        :: Maybe String
-  , optEnd          :: Maybe String
+  , optBegin        :: Maybe T.Text
+  , optEnd          :: Maybe T.Text
   , optInterval     :: Maybe Interval
   }
 
@@ -65,10 +66,10 @@
               (ReqArg (\a o -> o { optInterestAcc = a }) "ACCOUNT")
               "interest/gain/fees/losses account"
  , Option "b" ["begin"]
-              (ReqArg (\d o -> o { optBegin = Just d }) "DATE")
+              (ReqArg (\d o -> o { optBegin = Just (T.pack d) }) "DATE")
               "calculate interest from this date"
  , Option "e" ["end"]
-              (ReqArg (\d o -> o { optEnd = Just d }) "DATE")
+              (ReqArg (\d o -> o { optEnd = Just (T.pack d) }) "DATE")
               "calculate interest until this date"
  , Option "D" ["daily"]
               (NoArg (\o -> o { optInterval = Just (Days 1) }))
@@ -192,7 +193,7 @@
 
 -- | Convert a smart date string to a day using
 -- the provided reference date, or raise an error.
-fixSmartDateStr' :: Day -> String -> Day
+fixSmartDateStr' :: Day -> T.Text -> Day
 fixSmartDateStr' d s = either
                        (\e->error' $ printf "could not parse date %s %s" (show s) (show e))
                        id
diff --git a/hledger-irr.cabal b/hledger-irr.cabal
--- a/hledger-irr.cabal
+++ b/hledger-irr.cabal
@@ -1,5 +1,5 @@
 Name:                   hledger-irr
-Version:                0.1.1.8
+Version:                0.1.1.9
 Synopsis:               computes the internal rate of return of an investment
 License:                BSD3
 License-file:           LICENSE
@@ -11,7 +11,7 @@
 Tested-with:            GHC >= 7.4.1 && <= 7.4.1
 Description:
  hledger-irr is a small command-line utility based on Simon
- Michael's hleder library. Its purpose is to compute the internal rate of
+ Michael's hledger library. Its purpose is to compute the internal rate of
  return, also known as the effective interest rate, of a given investment.
  After specifying what account holds the investment, and what account stores
  the gains (or losses, or fees, or cost), it calculates the hypothetical
@@ -64,11 +64,11 @@
  > 2011/04/01: €-50.00
  > 2011/05/01: €47.00
  > 2011/06/01: €90.00
- > 2011/01/01 - 2015/10/31: -100.00%
+ > 2011/01/01 - 2016/10/27: -100.00%
  > $ hledger-irr -f speculation.ledger -t "Rate Gain" -i Speculation -e 2011-03-01
  > 2011/01/01 - 2011/03/01: 26.12%
  > $ hledger-irr -f speculation.ledger -t "Rate Gain" -i Speculation -b 2011-03-01
- > 2011/03/01 - 2015/10/31: -100.00%
+ > 2011/03/01 - 2016/10/27: -100.00%
  > $ hledger-irr -f speculation.ledger -t "Rate Gain" -i Speculation --monthly
  > 2011/01/01 - 2011/02/01: 12.49%
  > 2011/02/01 - 2011/03/01: 41.55%
@@ -104,7 +104,14 @@
 
 Executable hledger-irr
   Main-is:              Main.hs
-  Build-depends:        base >= 3 && < 5, hledger-lib >= 0.23.98 && < 0.28, Decimal, time, Cabal, statistics >= 0.10
+  Build-depends:
+    base >= 3 && < 5,
+    hledger-lib >= 1 && < 1.1,
+    Decimal,
+    time,
+    Cabal,
+    statistics >= 0.10,
+    text
   Ghc-Options:          -Wall
 
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