diff --git a/devtools/client/animationinspector/utils.js b/devtools/client/animationinspector/utils.js
index aa795f60865f..d791bbf1879c 100644
--- a/devtools/client/animationinspector/utils.js
+++ b/devtools/client/animationinspector/utils.js
@@ -328,7 +328,8 @@ var TimeScale = {
     // The width of the endDelay.
     let endDelayW = this.durationToDistance(Math.abs(endDelay) / rate);
     // The start position of the endDelay.
-    let endDelayX = endDelay < 0 ? x + w - endDelayW : x + w;
+    let endDelayX = endDelay < 0 ? x + iterationW - endDelayW
+                                 : x + iterationW;
 
     return {x, w, iterationW, delayX, delayW, negativeDelayW,
             endDelayX, endDelayW};