diff -r c8fe5ffdfe98 -r 4c502e3991bf src/java.net.http/share/classes/jdk/internal/net/http/frame/SettingsFrame.java
--- a/src/java.net.http/share/classes/jdk/internal/net/http/frame/SettingsFrame.java	Fri May 18 15:23:56 2018 +0100
+++ b/src/java.net.http/share/classes/jdk/internal/net/http/frame/SettingsFrame.java	Wed May 23 16:44:13 2018 +0100
@@ -110,14 +110,14 @@
         return TYPE;
     }
 
-    public int getParameter(int paramID) {
+    public synchronized int getParameter(int paramID) {
         if (paramID > MAX_PARAM) {
             throw new IllegalArgumentException("illegal parameter");
         }
         return parameters[paramID - 1];
     }
 
-    public SettingsFrame setParameter(int paramID, int value) {
+    public synchronized SettingsFrame setParameter(int paramID, int value) {
         if (paramID > MAX_PARAM) {
             throw new IllegalArgumentException("illegal parameter");
         }