diff --git a/compiler/types.nim b/compiler/types.nim
index ecbe371e2f..ab3395bc46 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -71,7 +71,7 @@ const
                tyInferred, tySink, tyLent, tyOwned}
   # typedescX is used if we're sure tyTypeDesc should be included (or skipped)
   typedescPtrs* = abstractPtrs + {tyTypeDesc}
-  typedescInst* = abstractInst + {tyTypeDesc, tyOwned}
+  typedescInst* = abstractInst + {tyTypeDesc, tyOwned, tyUserTypeClass}
 
 proc invalidGenericInst*(f: PType): bool =
   result = f.kind == tyGenericInst and lastSon(f) == nil