diff --git a/byg/byg.cabal b/byg/byg.cabal
index 4b1851b..9f7199e 100644
--- a/byg/byg.cabal
+++ b/byg/byg.cabal
@@ -17,4 +17,6 @@ executable byg
     import:           common
     main-is:          Main.hs
     hs-source-dirs:   src
-    build-depends:    base
+    build-depends:
+        base
+      , mtl