diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,11 @@
 # Revision history for greskell-core
 
+## 0.1.1.0  -- 2018-04-08
+
+* Add Semigroup instance to Greskell.
+* Confirmed test with base-4.11.
+
+
 ## 0.1.0.0  -- 2018-03-12
 
 * First version. Released on an unsuspecting world.
diff --git a/greskell-core.cabal b/greskell-core.cabal
--- a/greskell-core.cabal
+++ b/greskell-core.cabal
@@ -1,5 +1,5 @@
 name:                   greskell-core
-version:                0.1.0.0
+version:                0.1.1.0
 author:                 Toshio Ito <debug.ito@gmail.com>
 maintainer:             Toshio Ito <debug.ito@gmail.com>
 license:                BSD3
@@ -25,11 +25,12 @@
   exposed-modules:      Data.Greskell.Greskell,
                         Data.Greskell.GraphSON
   -- other-modules:        
-  build-depends:        base >=4.9.0.0 && <4.11,
+  build-depends:        base >=4.9.0.0 && <4.12,
                         aeson >=0.11.2.1 && <1.4,
                         unordered-containers >=0.2.7.1 && <0.3,
                         scientific >=0.3.4.9 && <0.4,
-                        text >=1.2.2.1 && <1.3
+                        text >=1.2.2.1 && <1.3,
+                        semigroups >=0.18.2 && <0.19
 
 test-suite spec
   type:                 exitcode-stdio-1.0
@@ -53,7 +54,7 @@
   ghc-options:          -Wall -fno-warn-unused-imports "-with-rtsopts=-M512m"
   main-is:              DocTest.hs
   build-depends:        base,
-                        doctest >=0.11 && <0.15,
+                        doctest >=0.11 && <0.16,
                         doctest-discover >=0.1.0.7 && <0.2
 
 
diff --git a/src/Data/Greskell/Greskell.hs b/src/Data/Greskell/Greskell.hs
--- a/src/Data/Greskell/Greskell.hs
+++ b/src/Data/Greskell/Greskell.hs
@@ -35,9 +35,10 @@
 import Data.Bifunctor (bimap)
 import Data.Foldable (toList)
 import qualified Data.HashMap.Lazy as HM
-import Data.Monoid (Monoid(..), (<>))
+import Data.Monoid (Monoid(..))
 import Data.Ratio (numerator, denominator, Rational)
 import Data.Scientific (Scientific, coefficient, base10Exponent)
+import Data.Semigroup (Semigroup(..))
 import Data.String (IsString(..))
 import Data.List (intersperse)
 import Data.Text (Text, pack, unpack)
@@ -83,12 +84,17 @@
     where
       scriptOf accessor = TL.pack $ show $ accessor rat
 
+-- | Semigroup operator '(<>)' on 'Greskell' assumes @String@
+-- concatenation on Gremlin.
+instance IsString a => Semigroup (Greskell a) where
+  (<>) = biOp "+"
+
 -- | Monoidal operations on 'Greskell' assumes @String@ operations in
 -- Gremlin. 'mempty' is the empty String, and 'mappend' is String
 -- concatenation.
 instance IsString a => Monoid (Greskell a) where
   mempty = fromString ""
-  mappend = biOp "+"
+  mappend = (<>)
 
 -- | Something that can convert to 'Greskell'.
 class ToGreskell a where