diff --git a/core/src/main/java/hudson/model/Hudson.java b/core/src/main/java/hudson/model/Hudson.java
index 75062e6bb5ea3022bbcbb780a4f9d7dc7f196435..f84e1b32ae0f0bc2916910e78c7c09ffb484f532 100644
--- a/core/src/main/java/hudson/model/Hudson.java
+++ b/core/src/main/java/hudson/model/Hudson.java
@@ -1964,7 +1964,7 @@ public final class Hudson extends View implements ItemGroup<TopLevelItem>, Node,
      */
     public void doIconSize( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException {
         String qs = req.getQueryString();
-        if(!ICON_SIZE.matcher(qs).matches())
+        if(qs==null || !ICON_SIZE.matcher(qs).matches())
             throw new ServletException();
         Cookie cookie = new Cookie("iconSize", qs);
         cookie.setMaxAge(/* ~4 mo. */9999999); // #762