diff --git a/Statistics/Distribution/Normal.hs b/Statistics/Distribution/Normal.hs
--- a/Statistics/Distribution/Normal.hs
+++ b/Statistics/Distribution/Normal.hs
@@ -127,5 +127,5 @@
   | p > 0 && p < 1 = x * ndCdfDenom d + mean d
   | otherwise      =
     error $ "Statistics.Distribution.Normal.quantile: p must be in [0,1] range. Got: "++show p
-  where x          = invErfc $ 2 * (1 - p)
+  where x          = - invErfc (2 * p)
         inf        = 1/0
diff --git a/Statistics/Test/WilcoxonT.hs b/Statistics/Test/WilcoxonT.hs
--- a/Statistics/Test/WilcoxonT.hs
+++ b/Statistics/Test/WilcoxonT.hs
@@ -11,7 +11,8 @@
 -- which could be used to whether two related samples have different
 -- means.
 --
--- WARNING: current implementation contain critical bugs
+-- WARNING: current implementation contain serious bug and couldn't be
+-- used with samples larger than 1023.
 -- <https://github.com/bos/statistics/issues/18>
 module Statistics.Test.WilcoxonT (
     -- * Wilcoxon signed-rank matched-pair test
diff --git a/statistics.cabal b/statistics.cabal
--- a/statistics.cabal
+++ b/statistics.cabal
@@ -1,5 +1,5 @@
 name:           statistics
-version:        0.11.0.2
+version:        0.11.0.3
 synopsis:       A library of statistical types, data, and functions
 description:
   This library provides a number of common functions and types useful