diff --git a/SecurityPkg/UserIdentification/UserProfileManagerDxe/UserProfileModify.c b/SecurityPkg/UserIdentification/UserProfileManagerDxe/UserProfileModify.c
index 67fc300f72..a0eb4afa9e 100644
--- a/SecurityPkg/UserIdentification/UserProfileManagerDxe/UserProfileModify.c
+++ b/SecurityPkg/UserIdentification/UserProfileManagerDxe/UserProfileModify.c
@@ -338,7 +338,7 @@ AddStr (
     StrLength = StrSize (Source2);
   } else {
     StrLength  = StrSize (*Source1);
-    StrLength += StrSize (Source2) -1;
+    StrLength += StrSize (Source2) - 2;
   }
 
   TmpStr     = AllocateZeroPool (StrLength);