diff --git a/arion-compose.cabal b/arion-compose.cabal
index ade58de..40a45be 100644
--- a/arion-compose.cabal
+++ b/arion-compose.cabal
@@ -38,6 +38,7 @@ common deps
                    , temporary
                    , text
                    , protolude
+                   , unix
 
 flag ghci
   default: False
diff --git a/src/haskell/exe/Main.hs b/src/haskell/exe/Main.hs
index f7c4035..fb29f89 100644
--- a/src/haskell/exe/Main.hs
+++ b/src/haskell/exe/Main.hs
@@ -22,9 +22,10 @@ import qualified Data.Text.Lazy.Builder as TB
 import qualified Data.List.NonEmpty as NE
 import Data.List.NonEmpty (NonEmpty(..))
 
-
 import Control.Arrow ((>>>))
 
+import System.Posix.User (getRealUserID)
+
 data CommonOptions =
   CommonOptions
     { files :: NonEmpty FilePath
@@ -159,14 +160,16 @@ runEvalAndDC cmd dopts opts = do
       }
 
 defaultEvaluationArgs :: CommonOptions -> IO EvaluationArgs
-defaultEvaluationArgs co = pure EvaluationArgs
-  { evalUid = 0 -- TODO
-  , evalModules = files co
-  , evalPkgs = pkgs co
-  , evalWorkDir = Nothing
-  , evalMode = ReadWrite
-  , evalUserArgs = nixArgs co
-  }
+defaultEvaluationArgs co = do
+  uid <- getRealUserID
+  pure EvaluationArgs
+    { evalUid = fromIntegral uid
+    , evalModules = files co
+    , evalPkgs = pkgs co
+    , evalWorkDir = Nothing
+    , evalMode = ReadWrite
+    , evalUserArgs = nixArgs co
+    }
 
 runCat :: CommonOptions -> IO ()
 runCat co = do