diff --git a/xpcom/string/public/nsTSubstring.h b/xpcom/string/public/nsTSubstring.h
index 808b74ac22c..f6c477859eb 100644
--- a/xpcom/string/public/nsTSubstring.h
+++ b/xpcom/string/public/nsTSubstring.h
@@ -183,12 +183,12 @@ class nsTSubstring_CharT : public nsTAString_CharT
 
       PRBool IsVoid() const
         {
-          return mFlags & F_VOIDED;
+          return (mFlags & F_VOIDED) != 0;
         }
 
       PRBool IsTerminated() const
         {
-          return mFlags & F_TERMINATED;
+          return (mFlags & F_TERMINATED) != 0;
         }
 
       char_type CharAt( index_type i ) const