diff --git a/string/obsolete/nsString.h b/string/obsolete/nsString.h
index f698cb05820..c7d1d00c2da 100644
--- a/string/obsolete/nsString.h
+++ b/string/obsolete/nsString.h
@@ -865,7 +865,10 @@ public:
 #if 0//def NEW_STRING_APIS
 NS_DEF_STRING_COMPARISON_OPERATORS(nsCAutoString, char)
 #endif
+
+#ifdef NEW_STRING_APIS
 NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsCAutoString, char)
+#endif
 
 /***************************************************************
   The subsumestr class is very unusual. 
diff --git a/string/obsolete/nsString2.h b/string/obsolete/nsString2.h
index 3cdbeae0268..620ad041d54 100644
--- a/string/obsolete/nsString2.h
+++ b/string/obsolete/nsString2.h
@@ -952,7 +952,9 @@ public:
     char mBuffer[kDefaultStringSize<<eTwoByte];
 };
 
+#ifdef NEW_STRING_APIS
 NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsAutoString, PRUnichar)
+#endif
 
 class NS_COM NS_ConvertASCIItoUCS2
       : public nsAutoString
diff --git a/xpcom/ds/nsString.h b/xpcom/ds/nsString.h
index f698cb05820..c7d1d00c2da 100644
--- a/xpcom/ds/nsString.h
+++ b/xpcom/ds/nsString.h
@@ -865,7 +865,10 @@ public:
 #if 0//def NEW_STRING_APIS
 NS_DEF_STRING_COMPARISON_OPERATORS(nsCAutoString, char)
 #endif
+
+#ifdef NEW_STRING_APIS
 NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsCAutoString, char)
+#endif
 
 /***************************************************************
   The subsumestr class is very unusual. 
diff --git a/xpcom/ds/nsString2.h b/xpcom/ds/nsString2.h
index 3cdbeae0268..620ad041d54 100644
--- a/xpcom/ds/nsString2.h
+++ b/xpcom/ds/nsString2.h
@@ -952,7 +952,9 @@ public:
     char mBuffer[kDefaultStringSize<<eTwoByte];
 };
 
+#ifdef NEW_STRING_APIS
 NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsAutoString, PRUnichar)
+#endif
 
 class NS_COM NS_ConvertASCIItoUCS2
       : public nsAutoString
diff --git a/xpcom/string/obsolete/nsString.h b/xpcom/string/obsolete/nsString.h
index f698cb05820..c7d1d00c2da 100644
--- a/xpcom/string/obsolete/nsString.h
+++ b/xpcom/string/obsolete/nsString.h
@@ -865,7 +865,10 @@ public:
 #if 0//def NEW_STRING_APIS
 NS_DEF_STRING_COMPARISON_OPERATORS(nsCAutoString, char)
 #endif
+
+#ifdef NEW_STRING_APIS
 NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsCAutoString, char)
+#endif
 
 /***************************************************************
   The subsumestr class is very unusual. 
diff --git a/xpcom/string/obsolete/nsString2.h b/xpcom/string/obsolete/nsString2.h
index 3cdbeae0268..620ad041d54 100644
--- a/xpcom/string/obsolete/nsString2.h
+++ b/xpcom/string/obsolete/nsString2.h
@@ -952,7 +952,9 @@ public:
     char mBuffer[kDefaultStringSize<<eTwoByte];
 };
 
+#ifdef NEW_STRING_APIS
 NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsAutoString, PRUnichar)
+#endif
 
 class NS_COM NS_ConvertASCIItoUCS2
       : public nsAutoString