--- a/layout/xul/base/src/tree/src/nsTreeBodyFrame.cpp
+++ b/layout/xul/base/src/tree/src/nsTreeBodyFrame.cpp
@@ -1544,18 +1544,18 @@ nsTreeBodyFrame::GetItemWithinCellAt(nsc
     // If we're the primary column, we have indentation and a twisty.
     PRInt32 level;
     mView->GetLevel(aRowIndex, &level);
 
     if (!isRTL)
       currX += mIndentation*level;
     remainingWidth -= mIndentation*level;
 
-    if (isRTL && aX > currX + remainingWidth ||
-        !isRTL && aX < currX) {
+    if ((isRTL && aX > currX + remainingWidth) ||
+        (!isRTL && aX < currX)) {
       // The user clicked within the indentation.
       return nsCSSAnonBoxes::moztreecell;
     }
 
     // Always leave space for the twisty.
     nsRect twistyRect(currX, cellRect.y, remainingWidth, cellRect.height);
     PRBool hasTwisty = PR_FALSE;
     PRBool isContainer = PR_FALSE;