diff --git a/jets/b/roll.c b/jets/b/roll.c
index 4700d3c99..1d047df48 100644
--- a/jets/b/roll.c
+++ b/jets/b/roll.c
@@ -18,8 +18,13 @@
     }
     else {
       u3_noun gim = u3k(u3h(a));
-      u3_noun zor = u3k(u3r_at(u3x_sam_3, b));
-      u3_noun daz = u3n_slam_on(u3k(b), u3nc(gim, zor));
+      u3_noun zor = u3r_at(u3x_sam, b);
+
+      if ( c3n == u3du(zor) ) {
+        return u3m_bail(c3__exit);
+      }
+
+      u3_noun daz = u3n_slam_on(u3k(b), u3nc(gim, u3k(u3t(zor))));
       u3_noun vel = u3i_molt(u3k(b), u3x_sam_3, daz, 0);
 
       if ( u3_none == vel ) {