diff --git a/intl/unicharutil/util/nsBidiUtils.cpp b/intl/unicharutil/util/nsBidiUtils.cpp
index 5af5e2620ead..111eb81a1db6 100644
--- a/intl/unicharutil/util/nsBidiUtils.cpp
+++ b/intl/unicharutil/util/nsBidiUtils.cpp
@@ -255,7 +255,7 @@ nsresult ArabicShaping(const PRUnichar* aString, PRUint32 aLen,
                        PRUnichar* aBuf, PRUint32 *aBufLen, 
                        PRBool aInputLogical, PRBool aOutputLogical)
 {
-  nsAutoString tempString(aString);
+  nsAutoString tempString(aString, aLen);
   PRUnichar *tempBuf = NS_CONST_CAST(PRUnichar*, tempString.get());
   if (aInputLogical) {
     ReverseString(tempBuf, aLen);