diff --git a/MdeModulePkg/Universal/CapsulePei/UefiCapsule.c b/MdeModulePkg/Universal/CapsulePei/UefiCapsule.c
index 3ac95b7be6..8d4ae69bb2 100644
--- a/MdeModulePkg/Universal/CapsulePei/UefiCapsule.c
+++ b/MdeModulePkg/Universal/CapsulePei/UefiCapsule.c
@@ -922,7 +922,7 @@ GetScatterGatherHeadEntries (
     if (Index != 0) {
       UnicodeValueToStringS (
         TempVarName,
-        (sizeof (CapsuleVarName) - ((StrLen (CapsuleVarName) + 1) * sizeof (CHAR16))),
+        (sizeof (CapsuleVarName) - ((UINTN)TempVarName - (UINTN)CapsuleVarName)),
         0,
         Index,
         0