diff --git a/egison.cabal b/egison.cabal
--- a/egison.cabal
+++ b/egison.cabal
@@ -7,7 +7,7 @@
 -- The package version. See the Haskell package versioning policy
 -- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for
 -- standards guiding when and how versions should be incremented.
-Version:             1.2.1
+Version:             1.2.2
 
 -- A short (one-line) description of the package.
 Synopsis:            An Interpreter for the Programming Language Egison
diff --git a/etc/lib/collection.egi b/etc/lib/collection.egi
--- a/etc/lib/collection.egi
+++ b/etc/lib/collection.egi
@@ -75,7 +75,7 @@
 (define $add
   (lambda [$a]
     (lambda [$xs $x]
-      (match ((member? Integer) x xs) Bool
+      (match ((member? a) x xs) Bool
         {[<true> xs]
          [<false> {@xs x}]}))))