diff --git a/dom/plugins/PluginInstanceChild.cpp b/dom/plugins/PluginInstanceChild.cpp
index 7d5c0dfedf59..ec01ce6eda53 100644
--- a/dom/plugins/PluginInstanceChild.cpp
+++ b/dom/plugins/PluginInstanceChild.cpp
@@ -59,6 +59,9 @@ using namespace mozilla::plugins;
 #elif defined(MOZ_WIDGET_QT)
 #include <QX11Info>
 #elif defined(OS_WIN)
+#ifndef WM_MOUSEHWHEEL
+#define WM_MOUSEHWHEEL     0x020E
+#endif
 
 #include "nsWindowsDllInterceptor.h"
 
@@ -1058,6 +1061,21 @@ PluginInstanceChild::PluginWindowProc(HWND hWnd,
     if (message == WM_MOUSEACTIVATE)
         self->CallPluginGotFocus();
 
+    // Prevent lockups due to plugins making rpc calls when the parent
+    // is making a synchronous SendMessage call to the child window. Add
+    // more messages as needed.
+    if ((InSendMessageEx(NULL)&(ISMEX_REPLIED|ISMEX_SEND)) == ISMEX_SEND) {
+        switch(message) {
+            case WM_KILLFOCUS:
+            case WM_MOUSEHWHEEL:
+            case WM_MOUSEWHEEL:
+            case WM_HSCROLL:
+            case WM_VSCROLL:
+            ReplyMessage(0);
+            break;
+        }
+    }
+
     if (message == WM_USER+1 &&
         (self->mQuirks & PluginInstanceChild::QUIRK_FLASH_THROTTLE_WMUSER_EVENTS)) {
         self->FlashThrottleMessage(hWnd, message, wParam, lParam, true);
diff --git a/dom/plugins/PluginModuleChild.cpp b/dom/plugins/PluginModuleChild.cpp
index 080aec15336b..d4cc5d692044 100644
--- a/dom/plugins/PluginModuleChild.cpp
+++ b/dom/plugins/PluginModuleChild.cpp
@@ -66,9 +66,6 @@
 using namespace mozilla::plugins;
 
 #if defined(XP_WIN)
-#ifndef WM_MOUSEHWHEEL
-#define WM_MOUSEHWHEEL     0x020E
-#endif
 const PRUnichar * kFlashFullscreenClass = L"ShockwaveFlashFullScreen";
 #endif
 
@@ -1903,60 +1900,16 @@ PluginModuleChild::CallWindowProcHook(int nCode, WPARAM wParam, LPARAM lParam)
     if (nCode >= 0 &&
         (InSendMessageEx(NULL)&(ISMEX_REPLIED|ISMEX_SEND)) == ISMEX_SEND) {
         CWPSTRUCT* pCwp = reinterpret_cast<CWPSTRUCT*>(lParam);
-        switch(pCwp->message) {
-            // Sync messages we can reply to:
-            case WM_SETFOCUS:
-            case WM_MOUSEHWHEEL:
-            case WM_MOUSEWHEEL:
-            case WM_HSCROLL:
-            case WM_VSCROLL:
-            case WM_CONTEXTMENU:
-            case WM_IME_SETCONTEXT:
-            case WM_WINDOWPOSCHANGED:
-                ReplyMessage(0);
-            break;
-            case WM_KILLFOCUS:
-            {
-                // Fix for flash fullscreen window loosing focus. On single
-                // core systems, sync killfocus events need to be handled
-                // after the flash fullscreen window procedure processes this
-                // message, otherwise fullscreen focus will not work correctly.
-                PRUnichar szClass[26];
-                if (GetClassNameW(pCwp->hwnd, szClass,
-                                  sizeof(szClass)/sizeof(PRUnichar)) &&
-                    !wcscmp(szClass, kFlashFullscreenClass)) {
-                    gDelayFlashFocusReplyUntilEval = true;
-                }
-                else {
-                    ReplyMessage(0);
-                }
-            }
-            break;
-            // Sync message that can't be handled:
-            case WM_WINDOWPOSCHANGING:
-            case WM_DESTROY:
-            case WM_PAINT:
-            break;
-            // Everything else:
-            default: {
-#ifdef DEBUG
-              nsCAutoString log("Child plugin module received untrapped ");
-              log.AppendLiteral("synchronous message for window. msg=");
-              char szTmp[40];
-              sprintf(szTmp, "0x%06X", pCwp->message);
-              log.Append(szTmp);
-              log.AppendLiteral(" hwnd=");
-              sprintf(szTmp, "0x%08X", pCwp->hwnd);
-              log.Append(szTmp);
-              PRUnichar className[256] = { 0 };
-              if (GetClassNameW(pCwp->hwnd, className,
-                                sizeof(className)/sizeof(PRUnichar)) > 0) {
-                  log.AppendLiteral(" class='");
-                  log.Append(NS_ConvertUTF16toUTF8((PRUnichar*)className));
-                  log.AppendLiteral("'");
-              }
-              NS_WARNING(log.get());
-#endif
+        if (pCwp->message == WM_KILLFOCUS) {
+            // Fix for flash fullscreen window loosing focus. On single
+            // core systems, sync killfocus events need to be handled
+            // after the flash fullscreen window procedure processes this
+            // message, otherwise fullscreen focus will not work correctly.
+            PRUnichar szClass[26];
+            if (GetClassNameW(pCwp->hwnd, szClass,
+                              sizeof(szClass)/sizeof(PRUnichar)) &&
+                !wcscmp(szClass, kFlashFullscreenClass)) {
+                gDelayFlashFocusReplyUntilEval = true;
             }
         }
     }