We see the following panic in this head.hackage [pipeline](https://gitlab.haskell.org/ghc/head.hackage/-/jobs/2213644) while compiling Agda. As far as I can tell, that's the first pipeline where it fails with this message, which corresponds to this commit: 3bf6720eff5e86e673568e756161e6d6150eb440 So it must have been introduced some time on that day ``` [252 of 433] Compiling Agda.TypeChecking.Serialise.Instances.Common ( src/full/Agda/TypeChecking/Serialise/Instances/Common.hs, dist/build/Agda/TypeChecking/Serialise/Instances/Common.o, dist/build/Agda/TypeChecking/Serialise/Instances/Common.dyn_o ) *** Parser [Agda.TypeChecking.Serialise.Instances.Common]: Parser [Agda.TypeChecking.Serialise.Instances.Common]: alloc=18062928 time=5.704 *** Renamer/typechecker [Agda.TypeChecking.Serialise.Instances.Common]: *** ConsistencyCheck [Agda.TypeChecking.Serialise.Instances.Common]: <no location info>: error: panic! (the 'impossible' happened) GHC version 9.13.20250626: expectJust Call stack: CallStack (from HasCallStack): pprPanic, called at compiler/GHC/Data/Maybe.hs:77:19 in ghc-9.13-07f9:GHC.Data.Maybe expectJustError, called at compiler/GHC/Data/Maybe.hs:74:24 in ghc-9.13-07f9:GHC.Data.Maybe expectJust, called at compiler/GHC/Tc/Instance/Family.hs:408:30 in ghc-9.13-07f9:GHC.Tc.Instance.Family Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug ```