--- a/src/java.net.http/share/classes/jdk/internal/net/http/Http2Connection.java	Fri Mar 02 10:18:48 2018 +0000
+++ b/src/java.net.http/share/classes/jdk/internal/net/http/Http2Connection.java	Fri Mar 02 15:14:03 2018 +0000
@@ -792,13 +792,16 @@
     {
         assert frame.streamid() == 0;
         if (!frame.getFlag(SettingsFrame.ACK)) {
-            int oldWindowSize = serverSettings.getParameter(INITIAL_WINDOW_SIZE);
             int newWindowSize = frame.getParameter(INITIAL_WINDOW_SIZE);
-            int diff = newWindowSize - oldWindowSize;
-            if (diff != 0) {
-                windowController.adjustActiveStreams(diff);
+            if (newWindowSize != -1) {
+                int oldWindowSize = serverSettings.getParameter(INITIAL_WINDOW_SIZE);
+                int diff = newWindowSize - oldWindowSize;
+                if (diff != 0) {
+                    windowController.adjustActiveStreams(diff);
+                }
             }
-            serverSettings = frame;
+
+            serverSettings.update(frame);
             sendFrame(new SettingsFrame(SettingsFrame.ACK));
         }
     }

--- a/src/java.net.http/share/classes/jdk/internal/net/http/WindowController.java	Fri Mar 02 10:18:48 2018 +0000
+++ b/src/java.net.http/share/classes/jdk/internal/net/http/WindowController.java	Fri Mar 02 15:14:03 2018 +0000
@@ -186,7 +186,9 @@
             if (size < 0)
                 return false;
             connectionWindowSize = size;
-            DEBUG_LOGGER.log(Level.DEBUG, "Connection window size is now %d", size);
+            DEBUG_LOGGER.log(Level.DEBUG,
+                    "Connection window size is now %d (amount added %d)",
+                    size, amount);
 
             // Notify waiting streams, until the new increased window size is
             // effectively exhausted.
@@ -244,7 +246,8 @@
                 return false;
             streams.put(streamid, size);
             DEBUG_LOGGER.log(Level.DEBUG,
-                             "Stream %s window size is now %s", streamid, size);
+                             "Stream %s window size is now %s (amount added %d)",
+                    streamid, size, amount);
 
             Map.Entry<Stream<?>,Integer> p = pending.get(streamid);
             if (p != null) {
@@ -286,7 +289,8 @@
                     size += adjustAmount;
                     streams.put(streamid, size);
                     DEBUG_LOGGER.log(Level.DEBUG,
-                        "Stream %s window size is now %s", streamid, size);
+                        "Stream %s window size is now %s (adjusting amount %d)",
+                            streamid, size, adjustAmount);
                 }
             }
         } finally {

--- a/src/java.net.http/share/classes/jdk/internal/net/http/frame/SettingsFrame.java	Fri Mar 02 10:18:48 2018 +0000
+++ b/src/java.net.http/share/classes/jdk/internal/net/http/frame/SettingsFrame.java	Fri Mar 02 15:14:03 2018 +0000
@@ -114,7 +114,7 @@
         if (paramID > MAX_PARAM) {
             throw new IllegalArgumentException("illegal parameter");
         }
-        return parameters[paramID-1];
+        return parameters[paramID - 1];
     }
 
     public SettingsFrame setParameter(int paramID, int value) {
@@ -153,6 +153,14 @@
 
     private static final int K = 1024;
 
+    public synchronized void update(SettingsFrame updated) {
+        for (int i = 0; i < MAX_PARAM; i++) {
+            if (updated.parameters[i] != -1) {
+                parameters[i] = updated.parameters[i];
+            }
+        }
+    }
+
     public static SettingsFrame getDefaultSettings() {
         SettingsFrame f = new SettingsFrame();
         // TODO: check these values