diff --git a/embedding/browser/powerplant/source/UMacUnicode.cpp b/embedding/browser/powerplant/source/UMacUnicode.cpp
index f3708ad5ef4e..6be30dd29d6d 100644
--- a/embedding/browser/powerplant/source/UMacUnicode.cpp
+++ b/embedding/browser/powerplant/source/UMacUnicode.cpp
@@ -102,13 +102,13 @@ void UMacUnicode::Str255ToString(const Str255& aStr255, nsString& aText)
 		PRInt32 outLength = 512;
 		rv = gUnicodeDecoder->Convert((char *) &aStr255[1], &inLength, buffer, &outLength);
 		if (NS_SUCCEEDED(rv)) {
-			aText.SetString(buffer, outLength);
+			aText.Assign(buffer, outLength);
 		}
 	}
 	
 	if (NS_FAILED(rv)) {
 //		NS_ASSERTION(0, "error: charset covnersion");
-		aText.SetString((char *) &aStr255[1], aStr255[0]);
+		aText.AssignWithConversion((char *) &aStr255[1], aStr255[0]);
 	}
 }
 
@@ -125,7 +125,7 @@ static void GetFileSystemCharset(nsString & fileSystemCharset)
 
     NS_ASSERTION(NS_SUCCEEDED(rv), "error getting platform charset");
 	  if (NS_FAILED(rv)) 
-		  aCharset.SetString("x-mac-roman");
+		  aCharset.AssignWithConversion("x-mac-roman");
   }
   fileSystemCharset = aCharset;
 }