diff --git a/lib/6to5/transformation/transformers/es7-abstract-references.js b/lib/6to5/transformation/transformers/es7-abstract-references.js
index 73d86adb7f..2bdf11365c 100644
--- a/lib/6to5/transformation/transformers/es7-abstract-references.js
+++ b/lib/6to5/transformation/transformers/es7-abstract-references.js
@@ -34,6 +34,17 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
     }
   }
 
+  if (node.operator !== "=") {
+    value = t.binaryExpression(
+      node.operator[0],
+      util.template("abstract-expression-get", {
+        PROPERTY: node.property,
+        OBJECT:   node.object
+      }),
+      value
+    );
+  }
+
   var call = util.template("abstract-expression-set", {
     PROPERTY: left.property,
     OBJECT:   left.object,