1 files changed, 5 insertions, 4 deletions
diff --git a/lib/pure/collections/critbits.nim b/lib/pure/collections/critbits.nim
index 34f5c5470..95fffdf88 100644
--- a/lib/pure/collections/critbits.nim
+++ b/lib/pure/collections/critbits.nim
@@ -74,18 +74,19 @@ proc rawInsert[T](c: var CritBitTree[T], key: string): Node[T] =
     var newByte = 0
     block blockX:
       while newbyte < key.len:
-        if it.key[newbyte] != key[newbyte]:
-          newotherbits = it.key[newbyte].ord xor key[newbyte].ord
+        let ch = if newbyte < it.key.len: it.key[newbyte] else: '\0'
+        if ch != key[newbyte]:
+          newotherbits = ch.ord xor key[newbyte].ord
           break blockX
         inc newbyte
-      if it.key[newbyte] != '\0':
+      if newbyte < it.key.len:
         newotherbits = it.key[newbyte].ord
       else:
         return it
     while (newOtherBits and (newOtherBits-1)) != 0:
       newOtherBits = newOtherBits and (newOtherBits-1)
     newOtherBits = newOtherBits xor 255
-    let ch = it.key[newByte]
+    let ch = if newByte < it.key.len: it.key[newByte] else: '\0'
     let dir = (1 + (ord(ch) or newOtherBits)) shr 8
 
     var inner: Node[T]