diff --git a/mozilla/layout/forms/nsComboboxControlFrame.cpp b/mozilla/layout/forms/nsComboboxControlFrame.cpp
index 8960b950672..af9a8efc104 100644
--- a/mozilla/layout/forms/nsComboboxControlFrame.cpp
+++ b/mozilla/layout/forms/nsComboboxControlFrame.cpp
@@ -307,7 +307,7 @@ nsComboboxControlFrame::nsComboboxControlFrame(nsStyleContext* aContext)
 
   mInRedisplayText = PR_FALSE;
 
-  mRecentSelectedIndex = -1;
+  mRecentSelectedIndex = NS_SKIP_NOTIFY_INDEX;
 
   //Shrink the area around its contents
   //SetFlags(NS_BLOCK_SHRINK_WRAP);
@@ -2007,7 +2007,7 @@ PRInt32
 nsComboboxControlFrame::UpdateRecentIndex(PRInt32 aIndex)
 {
   PRInt32 index = mRecentSelectedIndex;
-  if (mRecentSelectedIndex == -1 || aIndex == -1)
+  if (mRecentSelectedIndex == NS_SKIP_NOTIFY_INDEX || aIndex == NS_SKIP_NOTIFY_INDEX)
     mRecentSelectedIndex = aIndex;
   return index;
 }
diff --git a/mozilla/layout/forms/nsComboboxControlFrame.h b/mozilla/layout/forms/nsComboboxControlFrame.h
index c0dd7f05308..80d900a424a 100644
--- a/mozilla/layout/forms/nsComboboxControlFrame.h
+++ b/mozilla/layout/forms/nsComboboxControlFrame.h
@@ -52,6 +52,9 @@
 //#define DO_NEW_REFLOW
 #endif
 
+//Mark used to indicate when onchange has been fired for current combobox item
+#define NS_SKIP_NOTIFY_INDEX -2
+
 #include "nsAreaFrame.h"
 #include "nsIFormControlFrame.h"
 #include "nsIComboboxControlFrame.h"
diff --git a/mozilla/layout/forms/nsListControlFrame.cpp b/mozilla/layout/forms/nsListControlFrame.cpp
index 70a4cdc0aa2..d62e4a48015 100644
--- a/mozilla/layout/forms/nsListControlFrame.cpp
+++ b/mozilla/layout/forms/nsListControlFrame.cpp
@@ -1977,8 +1977,8 @@ nsListControlFrame::FireOnChange()
 {
   if (mComboboxFrame) {
     // Return hit without changing anything
-    PRInt32 index = mComboboxFrame->UpdateRecentIndex(-1);
-    if (index == -1)
+    PRInt32 index = mComboboxFrame->UpdateRecentIndex(NS_SKIP_NOTIFY_INDEX);
+    if (index == NS_SKIP_NOTIFY_INDEX)
       return;
 
     // See if the selection actually changed
@@ -2009,9 +2009,9 @@ NS_IMETHODIMP
 nsListControlFrame::OnSetSelectedIndex(PRInt32 aOldIndex, PRInt32 aNewIndex)
 {
   if (mComboboxFrame) {
-    // UpdateRecentIndex with -1, so that we won't fire an onchange
+    // UpdateRecentIndex with NS_SKIP_NOTIFY_INDEX, so that we won't fire an onchange
     // event for this setting of selectedIndex.
-    mComboboxFrame->UpdateRecentIndex(-1);
+    mComboboxFrame->UpdateRecentIndex(NS_SKIP_NOTIFY_INDEX);
   }
 
   ScrollToIndex(aNewIndex);