diff --git a/arvo/hoon.hoon b/arvo/hoon.hoon
index 56d56dc9f..81951edc4 100644
--- a/arvo/hoon.hoon
+++ b/arvo/hoon.hoon
@@ -1743,7 +1743,12 @@
   ~/  %rub
   |=  [a=@ b=@]
   ^-  [p=@ q=@]
-  =+  c==+(c=0 |-(?.(=(0 (cut 0 [(add a c) 1] b)) c $(c +(c)))))
+  =+  ^=  c
+      =+  [c=0 m=(met 0 b)]
+      |-  ?<  (gth c m)
+      ?.  =(0 (cut 0 [(add a c) 1] b))
+        c
+      $(c +(c))
   ?:  =(0 c)
     [1 0]
   =+  d=(add a +(c))