diff --git a/test/GHCup/ArbitraryTypes.hs b/test/GHCup/ArbitraryTypes.hs
index 1cfe13b..54dedfd 100644
--- a/test/GHCup/ArbitraryTypes.hs
+++ b/test/GHCup/ArbitraryTypes.hs
@@ -183,6 +183,10 @@ instance Arbitrary GHCupInfo where
   arbitrary = genericArbitrary
   shrink    = genericShrink
 
+instance Arbitrary GHCTargetVersion where
+  arbitrary = GHCTargetVersion Nothing <$> arbitrary
+  shrink    = genericShrink
+
 
 -- our maps are nested... the default size easily blows up most ppls ram