diff --git a/core/src/main/java/hudson/model/DownloadService.java b/core/src/main/java/hudson/model/DownloadService.java
index 0ea2f25cd762e660d7338ba3f8f58d82f87be8c6..0e918e1424b470c50f02f876881864535655d82b 100644
--- a/core/src/main/java/hudson/model/DownloadService.java
+++ b/core/src/main/java/hudson/model/DownloadService.java
@@ -39,6 +39,7 @@ import java.util.logging.Logger;
 
 import net.sf.json.JSONObject;
 import org.kohsuke.stapler.StaplerRequest;
+import org.kohsuke.stapler.StaplerResponse;
 
 /**
  * Service for plugins to periodically retrieve update data files
@@ -200,13 +201,14 @@ public class DownloadService extends PageDecorator {
         /**
          * This is where the browser sends us the data. 
          */
-        public void doPostBack(StaplerRequest req) throws IOException {
+        public void doPostBack(StaplerRequest req, StaplerResponse rsp) throws IOException {
             long dataTimestamp = System.currentTimeMillis();
             TextFile df = getDataFile();
             df.write(IOUtils.toString(req.getInputStream(),"UTF-8"));
             df.file.setLastModified(dataTimestamp);
             due = dataTimestamp+getInterval();
             LOGGER.info("Obtained the updated data file for "+id);
+            rsp.setContentType("text/plain");  // So browser won't try to parse response
         }
 
         /**
diff --git a/core/src/main/java/hudson/model/UpdateSite.java b/core/src/main/java/hudson/model/UpdateSite.java
index fd4c08e00b57a424609ffd1e6b456a4cee678698..863a5f2bb6994ef2c6fa146dc66cb177f0f814fc 100644
--- a/core/src/main/java/hudson/model/UpdateSite.java
+++ b/core/src/main/java/hudson/model/UpdateSite.java
@@ -134,7 +134,7 @@ public class UpdateSite {
     /**
      * This is the endpoint that receives the update center data file from the browser.
      */
-    public void doPostBack(StaplerRequest req) throws IOException, GeneralSecurityException {
+    public void doPostBack(StaplerRequest req, StaplerResponse rsp) throws IOException, GeneralSecurityException {
         dataTimestamp = System.currentTimeMillis();
         String json = IOUtils.toString(req.getInputStream(),"UTF-8");
         JSONObject o = JSONObject.fromObject(json);
@@ -150,6 +150,7 @@ public class UpdateSite {
 
         LOGGER.info("Obtained the latest update center data file for UpdateSource "+ id);
         getDataFile().write(json);
+        rsp.setContentType("text/plain");  // So browser won't try to parse response
     }
 
     /**