diff --git a/src/models/multiBar.js b/src/models/multiBar.js
index be97a11..e6d3e41 100644
--- a/src/models/multiBar.js
+++ b/src/models/multiBar.js
@@ -160,7 +160,7 @@ nv.models.multiBar = function() {
 
 
       var groups = wrap.select('.nv-groups').selectAll('.nv-group')
-          .data(function(d) { return d }, function(d) { return d.key });
+          .data(function(d) { return d }, function(d,i) { return i });
       groups.enter().append('g')
           .style('stroke-opacity', 1e-6)
           .style('fill-opacity', 1e-6);