diff --git a/src/org/opencms/flex/CmsFlexController.java b/src/org/opencms/flex/CmsFlexController.java
index <HASH>..<HASH> 100644
--- a/src/org/opencms/flex/CmsFlexController.java
+++ b/src/org/opencms/flex/CmsFlexController.java
@@ -375,7 +375,7 @@ public class CmsFlexController {
             // this resource can not be optimized for "last modified", use current time as header
             res.setDateHeader(CmsRequestUtil.HEADER_LAST_MODIFIED, System.currentTimeMillis());
             // avoiding issues with IE8+
-            res.setHeader(CmsRequestUtil.HEADER_CACHE_CONTROL, "public, max-age=0");
+            res.addHeader(CmsRequestUtil.HEADER_CACHE_CONTROL, "public, max-age=0");
         }
     }
Avoid overwriting already existent Cache-Control headers.