diff --git a/layout/forms/nsListControlFrame.cpp b/layout/forms/nsListControlFrame.cpp
index 0a86aab6d53d..b4fc25de1172 100644
--- a/layout/forms/nsListControlFrame.cpp
+++ b/layout/forms/nsListControlFrame.cpp
@@ -2895,7 +2895,6 @@ nsListControlFrame::MouseUp(nsIDOMEvent* aMouseEvent)
       mButtonDown = PR_FALSE;
       CaptureMouseEvents(mPresContext, PR_FALSE);
       SetContentSelected(mSelectedIndex, PR_FALSE);
-      mSelectedIndex = kNothingSelected;
       return NS_OK;
     }
   }
diff --git a/layout/html/forms/src/nsListControlFrame.cpp b/layout/html/forms/src/nsListControlFrame.cpp
index 0a86aab6d53d..b4fc25de1172 100644
--- a/layout/html/forms/src/nsListControlFrame.cpp
+++ b/layout/html/forms/src/nsListControlFrame.cpp
@@ -2895,7 +2895,6 @@ nsListControlFrame::MouseUp(nsIDOMEvent* aMouseEvent)
       mButtonDown = PR_FALSE;
       CaptureMouseEvents(mPresContext, PR_FALSE);
       SetContentSelected(mSelectedIndex, PR_FALSE);
-      mSelectedIndex = kNothingSelected;
       return NS_OK;
     }
   }