diff --git a/MdeModulePkg/Universal/DriverSampleDxe/DriverSample.c b/MdeModulePkg/Universal/DriverSampleDxe/DriverSample.c
index 83e669b9da..9751242fd2 100644
--- a/MdeModulePkg/Universal/DriverSampleDxe/DriverSample.c
+++ b/MdeModulePkg/Universal/DriverSampleDxe/DriverSample.c
@@ -444,10 +444,11 @@ CreateAltCfgString (
   EFI_STRING TmpStr;
   UINTN      NewLen;
 
+  NewLen = StrLen (Result);
   //
   // String Len = ConfigResp + AltConfig + AltConfig + 1("\0")
   //
-  NewLen = (StrLen (Result) + ((1 + StrLen (ConfigHdr) + 8 + 4) + (8 + 4 + 7 + 4 + 7 + 4)) * 2 + 1) * sizeof (CHAR16);
+  NewLen = (NewLen + ((1 + StrLen (ConfigHdr) + 8 + 4) + (8 + 4 + 7 + 4 + 7 + 4)) * 2 + 1) * sizeof (CHAR16);
   StringPtr = AllocateZeroPool (NewLen);
   if (StringPtr == NULL) {
     return NULL;