diff --git a/widget/windows/nsTextStore.cpp b/widget/windows/nsTextStore.cpp
index ad48e794be7..cb583d90395 100644
--- a/widget/windows/nsTextStore.cpp
+++ b/widget/windows/nsTextStore.cpp
@@ -963,6 +963,15 @@ nsTextStore::DidLockGranted()
     mNativeCaretIsCreated = false;
   }
   if (IsReadWriteLocked()) {
+    if (IsPendingCompositionUpdateIncomplete()) {
+      // FreeCJ (TIP for Traditional Chinese) calls SetSelection() to set caret
+      // to the start of composition string and insert a full width space for
+      // a placeholder with a call of SetText().  After that, it calls
+      // OnUpdateComposition() without new range.  Therefore, let's record the
+      // composition update information here.
+      RecordCompositionUpdateAction();
+    }
+
     FlushPendingActions();
   }
 
@@ -1621,7 +1630,7 @@ nsTextStore::RecordCompositionUpdateAction()
     return E_FAIL;
   }
 
-  PendingAction* action = GetPendingCompositionUpdate();
+  PendingAction* action = LastOrNewPendingCompositionUpdate();
   action->mData = mComposition.mString;
   // The ranges might already have been initialized, however, if this is
   // called again, that means we need to overwrite the ranges with current
@@ -1714,6 +1723,8 @@ nsTextStore::RecordCompositionUpdateAction()
   caretRange.mRangeType = NS_TEXTRANGE_CARETPOSITION;
   action->mRanges->AppendElement(caretRange);
 
+  action->mIncomplete = false;
+
   PR_LOG(sTextStoreLog, PR_LOG_ALWAYS,
          ("TSF: 0x%p   nsTextStore::RecordCompositionUpdateAction() "
           "succeeded", this));
@@ -2925,6 +2936,8 @@ nsTextStore::OnUpdateComposition(ITfCompositionView* pComposition,
 
   // pRangeNew is null when the update is not complete
   if (!pRangeNew) {
+    PendingAction* action = LastOrNewPendingCompositionUpdate();
+    action->mIncomplete = true;
     PR_LOG(sTextStoreLog, PR_LOG_ALWAYS,
            ("TSF: 0x%p   nsTextStore::OnUpdateComposition() succeeded but "
             "not complete", this));
diff --git a/widget/windows/nsTextStore.h b/widget/windows/nsTextStore.h
index 43b2a2e0518..48aa3a464be 100644
--- a/widget/windows/nsTextStore.h
+++ b/widget/windows/nsTextStore.h
@@ -506,6 +506,8 @@ protected:
     nsRefPtr<mozilla::TextRangeArray> mRanges;
     // For selectionset
     bool mSelectionReversed;
+    // For compositionupdate
+    bool mIncomplete;
   };
   // Items of mPendingActions are appended when TSF tells us to need to dispatch
   // DOM composition events.  However, we cannot dispatch while the document is
@@ -513,7 +515,7 @@ protected:
   // actions should be performed when document lock is unlocked.
   nsTArray<PendingAction> mPendingActions;
 
-  PendingAction* GetPendingCompositionUpdate()
+  PendingAction* LastOrNewPendingCompositionUpdate()
   {
     if (!mPendingActions.IsEmpty()) {
       PendingAction& lastAction = mPendingActions.LastElement();
@@ -524,9 +526,20 @@ protected:
     PendingAction* newAction = mPendingActions.AppendElement();
     newAction->mType = PendingAction::COMPOSITION_UPDATE;
     newAction->mRanges = new mozilla::TextRangeArray();
+    newAction->mIncomplete = true;
     return newAction;
   }
 
+  bool IsPendingCompositionUpdateIncomplete() const
+  {
+    if (mPendingActions.IsEmpty()) {
+      return false;
+    }
+    const PendingAction& lastAction = mPendingActions.LastElement();
+    return lastAction.mType == PendingAction::COMPOSITION_UPDATE &&
+           lastAction.mIncomplete;
+  }
+
   // When On*Composition() is called without document lock, we need to flush
   // the recorded actions at quitting the method.
   // AutoPendingActionAndContentFlusher class is usedful for it.