diff --git a/tinygrad/uop/symbolic.py b/tinygrad/uop/symbolic.py
index 6e21233106..5a379c340a 100644
--- a/tinygrad/uop/symbolic.py
+++ b/tinygrad/uop/symbolic.py
@@ -24,14 +24,15 @@ def fold_bitcast(root:UOp, c:UOp) -> UOp|None:
 invalid_pat = UPat(Ops.CONST, arg=Invalid, name="i")
 invalid_gate = UPat.var("cond").where(UPat.var("x"), invalid_pat)
 
+# this needs to be before symbolic so that 0*something_that_might_be_invalid doesnt become 0
 propagate_invalid = PatternMatcher([
-  # this needs to be before symbolic so that 0*something_that_might_be_invalid doesnt become 0
   # propagate invalid, push it past children
-  (invalid_gate.cast(name="cast"), lambda i,x,cond,cast: x.cast(cast.dtype) if cast.dtype is not dtypes.index else None),
+  (invalid_gate.cast(name="cast"), lambda i,x,cond,cast: x.cast(cast.dtype)),
   *((invalid_gate.alu(op, UPat.var("y")).named("alu"), lambda cond,x,y,alu,i: cond.where(x.alu(alu.op,y), i))
     for op in GroupOp.Binary-GroupOp.Comparison),
+  # TODO: when can this happen? and is it always safe to just drop invalid?
   *((invalid_gate.alu(op, UPat.var("y")).named("alu"), lambda cond,x,y,alu,i: x.alu(alu.op,y)) for op in GroupOp.Comparison),
-  # invalid + y -> y same for other ops
+  # invalid + y -> invalid same for other ops
   *((invalid_pat.alu(op, UPat(dtype=dtypes.index)).named("alu"), lambda alu,i: i) for op in GroupOp.Binary-GroupOp.Comparison),
   # a.where(b.where(c, d), d) -> (a & b).where(c, d)
   (UPat.var("a").where(UPat.var("b").where(UPat.var("c"), UPat.var("d")), UPat.var("d")), lambda a,b,c,d: (a&b).where(c,d)),