diff --git a/Command.cabal b/Command.cabal
--- a/Command.cabal
+++ b/Command.cabal
@@ -1,5 +1,5 @@
 Name:               Command
-Version:            0.0.5
+Version:            0.0.6
 License:            BSD3
 License-File:       LICENSE
 Author:             Tony Morris <ʇǝu˙sıɹɹoɯʇ@ןןǝʞsɐɥ>
diff --git a/src/System/Command.hs b/src/System/Command.hs
--- a/src/System/Command.hs
+++ b/src/System/Command.hs
@@ -173,7 +173,7 @@
 --
 -- Only if the result is successful, run the second action returning no result.
 (->>>) ::
-  Monad m =>
+  (Monad m, Functor m) =>
   m ExitCode
   -> m a
   -> m ()
@@ -208,7 +208,7 @@
 --
 -- Only if the result is successful, run the first action returning no result.
 (<<<-) ::
-  Monad m =>
+  (Monad m, Functor m) =>
   m a
   -> m ExitCode
   -> m ()