diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,10 @@
 # Revision history for staversion
 
+## 0.2.1.4  -- 2018-03-26
+
+* Support `base-4.11.0.0`.
+
+
 ## 0.2.1.3  -- 2018-03-09
 
 * Support `aeson-1.3.0.0`, `base-4.10.0.0`, `Cabal-2.2.0.0`,
diff --git a/src/Staversion/Internal/BuildPlan.hs b/src/Staversion/Internal/BuildPlan.hs
--- a/src/Staversion/Internal/BuildPlan.hs
+++ b/src/Staversion/Internal/BuildPlan.hs
@@ -32,6 +32,7 @@
 import qualified Data.HashMap.Strict as HM
 import Data.IORef (IORef, newIORef, readIORef, writeIORef)
 import Data.Monoid (Monoid, (<>), mconcat)
+import Data.Semigroup (Semigroup)
 import Data.Text (Text, unpack)
 import Data.Traversable (Traversable(traverse))
 import Data.Word (Word)
@@ -66,7 +67,7 @@
 
 -- | A data structure that keeps a map between package names and their
 -- versions.
-newtype BuildPlanMap = BuildPlanMap (HM.HashMap PackageName Version) deriving (Monoid)
+newtype BuildPlanMap = BuildPlanMap (HM.HashMap PackageName Version) deriving (Semigroup,Monoid)
 
 instance FromJSON BuildPlanMap where
   parseJSON (Object object) = (\p1 p2 -> BuildPlanMap $ p1 <> p2) <$> core_packages <*> other_packages where
diff --git a/staversion.cabal b/staversion.cabal
--- a/staversion.cabal
+++ b/staversion.cabal
@@ -1,5 +1,5 @@
 name:                   staversion
-version:                0.2.1.3
+version:                0.2.1.4
 author:                 Toshio Ito <debug.ito@gmail.com>
 maintainer:             Toshio Ito <debug.ito@gmail.com>
 license:                BSD3
@@ -47,7 +47,7 @@
   other-modules:        Paths_staversion,
                         Staversion.Internal.HTTP,
                         Staversion.Internal.Megaparsec
-  build-depends:        base >=4.8 && <4.11,
+  build-depends:        base >=4.8 && <4.12,
                         unordered-containers >=0.2.3 && <0.3,
                         aeson >=0.8.0 && <1.4,
                         text >=0.11.3 && <1.3,