diff --git a/web/time-wasting-thread-memorial.cabal b/web/time-wasting-thread-memorial.cabal
index 42992b2..de3a315 100644
--- a/web/time-wasting-thread-memorial.cabal
+++ b/web/time-wasting-thread-memorial.cabal
@@ -67,6 +67,7 @@ executable time-wasting-thread-memorial
                      , wai-extra >=1.3.0
                      , pandoc >=1.15.0.6
                      , mtl >=2.2.1
+                     , containers >=0.5.0.0
 
   -- Directories containing source files.
   hs-source-dirs:      src