diff --git a/pkgs/development/haskell-modules/non-hackage-packages.nix b/pkgs/development/haskell-modules/non-hackage-packages.nix
index 092af07637f..9a2ff6f4a2a 100644
--- a/pkgs/development/haskell-modules/non-hackage-packages.nix
+++ b/pkgs/development/haskell-modules/non-hackage-packages.nix
@@ -8,7 +8,7 @@
 self: super: {
 
   multi-ghc-travis = throw ("haskellPackages.multi-ghc-travis has been renamed"
-    + "to haskell-ci, which is now on hackage");
+    + " to haskell-ci, which is now on hackage");
 
   # https://github.com/channable/vaultenv/issues/1
   vaultenv = self.callPackage ../tools/haskell/vaultenv { };