diff --git a/layout/xul/base/src/nsTextBoxFrame.cpp b/layout/xul/base/src/nsTextBoxFrame.cpp
index 88fef28259f8..9a6ce1c977cc 100644
--- a/layout/xul/base/src/nsTextBoxFrame.cpp
+++ b/layout/xul/base/src/nsTextBoxFrame.cpp
@@ -707,7 +707,7 @@ nsTextBoxFrame::UpdateAccessTitle()
                 || AlwaysAppendAccessKey()) 
             {
                 nsAutoString tmpstring;
-                if (!mTitle.IsEmpty() && !isspace(mTitle.Last())) {
+                if (!mTitle.IsEmpty() && !NS_IS_SPACE(mTitle.Last())) {
                   tmpstring += ' ';
                 }
                 tmpstring += '(';