diff --git a/tests/tcustom.nim b/tests/tcustom.nim
index 647d8bf..01e0114 100644
--- a/tests/tcustom.nim
+++ b/tests/tcustom.nim
@@ -69,7 +69,7 @@ proc mutateMatrix32[M, N: static[int]](value: sink Matrix32[M, N]; r: var Rand):
 proc mutate[M, N: static[int]](value: var Matrix32[M, N]; sizeIncreaseHint: int; enforceChanges: bool; r: var Rand) =
   repeatMutate(mutateMatrix32(move value, r))
 
-func fuzzTarget(x: Matrix32[2, 1]) =
+proc fuzzTarget(x: Matrix32[2, 1]) =
   doAssert x != ones(2, 1)
 
 defaultMutator(fuzzTarget)