diff --git a/src/main/java/hudson/tasks/junit/History.java b/src/main/java/hudson/tasks/junit/History.java
index b6aaece38..629810214 100644
--- a/src/main/java/hudson/tasks/junit/History.java
+++ b/src/main/java/hudson/tasks/junit/History.java
@@ -73,8 +73,8 @@ public boolean historyAvailable() {
 
     @JavaScriptMethod
     @SuppressWarnings("unused") // Called by jelly view
-    public String getTestResultTrend() {
-        return JACKSON_FACADE.toJson(createTestResultTrend());
+    public LinesChartModel getTestResultTrend() {
+        return createTestResultTrend();
     }
 
     private LinesChartModel createTestResultTrend() {
@@ -88,8 +88,8 @@ private LinesChartModel createTestResultTrend() {
 
     @JavaScriptMethod
     @SuppressWarnings("unused") // Called by jelly view
-    public String getTestDurationTrend() {
-        return JACKSON_FACADE.toJson(createTestDurationResultTrend());
+    public LinesChartModel getTestDurationTrend() {
+        return createTestDurationResultTrend();
     }
 
     private LinesChartModel createTestDurationResultTrend() {
diff --git a/src/main/webapp/history/history.js b/src/main/webapp/history/history.js
index 10f75e16d..4d4b68b02 100644
--- a/src/main/webapp/history/history.js
+++ b/src/main/webapp/history/history.js
@@ -14,7 +14,7 @@ document.addEventListener('DOMContentLoaded', function () {
          * Requires that a DOM <div> element exists with the ID '#test-duration-trend-chart'.
          */
         view.getTestDurationTrend(function (lineModel) {
-            echartsJenkinsApi.renderZoomableTrendChart('test-duration-trend-chart', lineModel.responseJSON, redrawTrendCharts);
+            echartsJenkinsApi.renderZoomableTrendChart('test-duration-trend-chart', lineModel.responseText, redrawTrendCharts);
         });
 
         /**
@@ -22,7 +22,7 @@ document.addEventListener('DOMContentLoaded', function () {
          * Requires that a DOM <div> element exists with the ID '#test-result-trend-chart'.
          */
         view.getTestResultTrend(function (lineModel) {
-            echartsJenkinsApi.renderZoomableTrendChart('test-result-trend-chart', lineModel.responseJSON, redrawTrendCharts);
+            echartsJenkinsApi.renderZoomableTrendChart('test-result-trend-chart', lineModel.responseText, redrawTrendCharts);
         });
     }