From b58fbd1b48bd0e0eaf334422d84ad7cd9238f243 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Tue, 28 Mar 2017 20:57:34 +0200
Subject: [PATCH] fixes #5618

---
 compiler/transf.nim | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/compiler/transf.nim b/compiler/transf.nim
index 771dc58f44..41959b0185 100644
--- a/compiler/transf.nim
+++ b/compiler/transf.nim
@@ -566,7 +566,10 @@ proc transformFor(c: PTransf, n: PNode): PTransNode =
   pushTransCon(c, newC)
   for i in countup(1, sonsLen(call) - 1):
     var arg = transform(c, call.sons[i]).PNode
-    var formal = skipTypes(iter.typ, abstractInst).n.sons[i].sym
+    let ff = skipTypes(iter.typ, abstractInst)
+    # can happen for 'nim check':
+    if i >= ff.n.len: return result
+    var formal = ff.n.sons[i].sym
     case putArgInto(arg, formal.typ)
     of paDirectMapping:
       idNodeTablePut(newC.mapping, formal, arg)