diff --git a/src/config.js b/src/config.js
index 1353ec005..f9ceb137d 100644
--- a/src/config.js
+++ b/src/config.js
@@ -137,6 +137,12 @@ const config = {
    * The object containing configurations specific for sequence diagrams
    */
   sequence: {
+    /**
+     * widt of the activation rect
+     * **Default value 10**.
+     */
+    activationWidth: 10,
+
     /**
      * margin to the right and left of the sequence diagram.
      * **Default value 50**.
diff --git a/src/diagrams/sequence/sequenceRenderer.js b/src/diagrams/sequence/sequenceRenderer.js
index 09e33b1a6..a05415f02 100644
--- a/src/diagrams/sequence/sequenceRenderer.js
+++ b/src/diagrams/sequence/sequenceRenderer.js
@@ -1002,8 +1002,8 @@ const calculateLoopBounds = function(messages, actors) {
         break;
       case parser.yy.LINETYPE.ACTIVE_START:
         {
-          const actorRect = actors[msg.from.actor];
-          const stackedSize = actorActivations(msg.from.actor).length;
+          const actorRect = actors[msg.from ? msg.from.actor : msg.to.actor];
+          const stackedSize = actorActivations(msg.from ? msg.from.actor : msg.to.actor).length;
           const x =
             actorRect.x + actorRect.width / 2 + ((stackedSize - 1) * conf.activationWidth) / 2;
           const toAdd = {