diff --git a/haskdogs.cabal b/haskdogs.cabal
--- a/haskdogs.cabal
+++ b/haskdogs.cabal
@@ -1,5 +1,5 @@
 Name:                haskdogs
-Version:             0.4.4
+Version:             0.4.5
 Synopsis:            Generate tags file for Haskell project and its nearest deps
 Homepage:            http://github.com/grwlf/haskdogs
 License:             BSD3
diff --git a/src/Main.hs b/src/Main.hs
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -11,6 +11,7 @@
 import System.Process (readProcess)
 import System.FilePath
 
+import Data.Monoid((<>))
 import Data.Set (Set)
 import qualified Data.Set as Set
 import Options.Applicative