diff --git a/base/src/nsString.cpp b/base/src/nsString.cpp
index 72a033a4df0..ed6377962e2 100644
--- a/base/src/nsString.cpp
+++ b/base/src/nsString.cpp
@@ -419,6 +419,16 @@ PRUnichar& nsString::Last() const{
   else return gBadChar;
 }
 
+PRBool nsString::SetCharAt(PRUnichar aChar,PRInt32 anIndex){
+  PRBool result=PR_FALSE;
+  if(anIndex<mLength){
+    PRUnichar* theStr=(PRUnichar*)mStr;
+    theStr[anIndex]=aChar;
+    result=PR_TRUE;
+  }
+  return result;
+}
+
 /**
  * Create a new string by appending given string to this
  * @update	gess 7/27/98
diff --git a/base/src/nsString.h b/base/src/nsString.h
index 38ee3929bab..9c26190660b 100644
--- a/base/src/nsString.h
+++ b/base/src/nsString.h
@@ -171,6 +171,9 @@ PRUnichar& First() const;
  */
 PRUnichar& Last() const;
 
+PRBool SetCharAt(PRUnichar aChar,PRInt32 anIndex);
+
+
 /**********************************************************************
   String creation methods...
  *********************************************************************/
diff --git a/rdf/base/src/nsRDFXMLDataSource.cpp b/rdf/base/src/nsRDFXMLDataSource.cpp
index df7bc1effc0..1c309b81ca2 100644
--- a/rdf/base/src/nsRDFXMLDataSource.cpp
+++ b/rdf/base/src/nsRDFXMLDataSource.cpp
@@ -983,12 +983,12 @@ rdf_EscapeAngleBrackets(nsString& s)
 {
     PRInt32 index;
     while ((index = s.Find('<')) != -1) {
-        s[index] = '&';
+        s.SetCharAt('&',index);
         s.Insert(nsAutoString("lt;"), index + 1);
     }
 
     while ((index = s.Find('>')) != -1) {
-        s[index] = '&';
+        s.SetCharAt('&',index);
         s.Insert(nsAutoString("gt;"), index + 1);
     }
 }
@@ -998,7 +998,7 @@ rdf_EscapeAmpersands(nsString& s)
 {
     PRInt32 index = 0;
     while ((index = s.Find('&', index)) != -1) {
-        s[index] = '&';
+        s.SetCharAt('&',index);
         s.Insert(nsAutoString("amp;"), index + 1);
         index += 4;
     }
diff --git a/rdf/datasource/src/nsBookmarkDataSource.cpp b/rdf/datasource/src/nsBookmarkDataSource.cpp
index 2f4981025b4..fb71fc991ba 100644
--- a/rdf/datasource/src/nsBookmarkDataSource.cpp
+++ b/rdf/datasource/src/nsBookmarkDataSource.cpp
@@ -277,7 +277,7 @@ BookmarkParser::ParseBookmark(const nsString& aLine, nsIRDFResource* aContainer)
         static const char kEscape22[] = "%22";
         PRInt32 offset;
         while ((offset = url.Find(kEscape22)) >= 0) {
-            url[offset] = PRUnichar(' ');
+            url.SetCharAt(' ',offset);
             url.Cut(offset + 1, sizeof(kEscape22) - 2);
         }
     }
diff --git a/string/obsolete/nsString.cpp b/string/obsolete/nsString.cpp
index 72a033a4df0..ed6377962e2 100644
--- a/string/obsolete/nsString.cpp
+++ b/string/obsolete/nsString.cpp
@@ -419,6 +419,16 @@ PRUnichar& nsString::Last() const{
   else return gBadChar;
 }
 
+PRBool nsString::SetCharAt(PRUnichar aChar,PRInt32 anIndex){
+  PRBool result=PR_FALSE;
+  if(anIndex<mLength){
+    PRUnichar* theStr=(PRUnichar*)mStr;
+    theStr[anIndex]=aChar;
+    result=PR_TRUE;
+  }
+  return result;
+}
+
 /**
  * Create a new string by appending given string to this
  * @update	gess 7/27/98
diff --git a/string/obsolete/nsString.h b/string/obsolete/nsString.h
index 38ee3929bab..9c26190660b 100644
--- a/string/obsolete/nsString.h
+++ b/string/obsolete/nsString.h
@@ -171,6 +171,9 @@ PRUnichar& First() const;
  */
 PRUnichar& Last() const;
 
+PRBool SetCharAt(PRUnichar aChar,PRInt32 anIndex);
+
+
 /**********************************************************************
   String creation methods...
  *********************************************************************/
diff --git a/xpcom/ds/nsString.cpp b/xpcom/ds/nsString.cpp
index 72a033a4df0..ed6377962e2 100644
--- a/xpcom/ds/nsString.cpp
+++ b/xpcom/ds/nsString.cpp
@@ -419,6 +419,16 @@ PRUnichar& nsString::Last() const{
   else return gBadChar;
 }
 
+PRBool nsString::SetCharAt(PRUnichar aChar,PRInt32 anIndex){
+  PRBool result=PR_FALSE;
+  if(anIndex<mLength){
+    PRUnichar* theStr=(PRUnichar*)mStr;
+    theStr[anIndex]=aChar;
+    result=PR_TRUE;
+  }
+  return result;
+}
+
 /**
  * Create a new string by appending given string to this
  * @update	gess 7/27/98
diff --git a/xpcom/ds/nsString.h b/xpcom/ds/nsString.h
index 38ee3929bab..9c26190660b 100644
--- a/xpcom/ds/nsString.h
+++ b/xpcom/ds/nsString.h
@@ -171,6 +171,9 @@ PRUnichar& First() const;
  */
 PRUnichar& Last() const;
 
+PRBool SetCharAt(PRUnichar aChar,PRInt32 anIndex);
+
+
 /**********************************************************************
   String creation methods...
  *********************************************************************/
diff --git a/xpcom/string/obsolete/nsString.cpp b/xpcom/string/obsolete/nsString.cpp
index 72a033a4df0..ed6377962e2 100644
--- a/xpcom/string/obsolete/nsString.cpp
+++ b/xpcom/string/obsolete/nsString.cpp
@@ -419,6 +419,16 @@ PRUnichar& nsString::Last() const{
   else return gBadChar;
 }
 
+PRBool nsString::SetCharAt(PRUnichar aChar,PRInt32 anIndex){
+  PRBool result=PR_FALSE;
+  if(anIndex<mLength){
+    PRUnichar* theStr=(PRUnichar*)mStr;
+    theStr[anIndex]=aChar;
+    result=PR_TRUE;
+  }
+  return result;
+}
+
 /**
  * Create a new string by appending given string to this
  * @update	gess 7/27/98
diff --git a/xpcom/string/obsolete/nsString.h b/xpcom/string/obsolete/nsString.h
index 38ee3929bab..9c26190660b 100644
--- a/xpcom/string/obsolete/nsString.h
+++ b/xpcom/string/obsolete/nsString.h
@@ -171,6 +171,9 @@ PRUnichar& First() const;
  */
 PRUnichar& Last() const;
 
+PRBool SetCharAt(PRUnichar aChar,PRInt32 anIndex);
+
+
 /**********************************************************************
   String creation methods...
  *********************************************************************/