diff --git a/MdePkg/Library/BaseLib/String.c b/MdePkg/Library/BaseLib/String.c
index e7fe513aec..cb90774c86 100644
--- a/MdePkg/Library/BaseLib/String.c
+++ b/MdePkg/Library/BaseLib/String.c
@@ -1262,7 +1262,7 @@ AsciiStriCmp (
 
   UpperFirstString  = InternalBaseLibAsciiToUpper (*FirstString);
   UpperSecondString = InternalBaseLibAsciiToUpper (*SecondString);
-  while ((*FirstString != '\0') && (UpperFirstString == UpperSecondString)) {
+  while ((*FirstString != '\0') && (*SecondString != '\0') && (UpperFirstString == UpperSecondString)) {
     FirstString++;
     SecondString++;
     UpperFirstString  = InternalBaseLibAsciiToUpper (*FirstString);