diff --git a/shake-ats.cabal b/shake-ats.cabal
--- a/shake-ats.cabal
+++ b/shake-ats.cabal
@@ -1,5 +1,5 @@
 name:                shake-ats
-version:             1.3.0.5
+version:             1.3.0.6
 synopsis:            Utilities for building ATS projects with shake
 description:         Various helper functions for building [ATS](http://www.ats-lang.org/) with the [shake](http://shakebuild.com/) library
 homepage:            https://github.com/vmchale/shake-ats#readme
diff --git a/src/Development/Shake/ATS.hs b/src/Development/Shake/ATS.hs
--- a/src/Development/Shake/ATS.hs
+++ b/src/Development/Shake/ATS.hs
@@ -128,8 +128,8 @@
         let toLibs = fmap ("-l" <>)
         let libs' = ("atslib" :) $ bool libs ("gc" : libs) gc
         ghcV <- case hsLibs of
-            [] -> pure mempty
-            _  -> ghcVersion -- FIXME call on ghc specified?
+            [] -> pure undefined
+            _  -> ghcVersion
         command
             [EchoStderr False, AddEnv "PATSHOME" home, AddEnv "PATH" (home ++ "/bin:" ++ path), AddEnv "PATSHOMELOCS" $ patsHomeLocs 5]
             (home ++ "/bin/patscc")