diff --git a/MdePkg/Library/BaseLib/String.c b/MdePkg/Library/BaseLib/String.c
index 80223c6732..a59a9d08cb 100644
--- a/MdePkg/Library/BaseLib/String.c
+++ b/MdePkg/Library/BaseLib/String.c
@@ -713,6 +713,10 @@ AsciiStrnCmp (
   IN      UINTN                     Length
   )
 {
+  if (Length == 0) {
+    return 0;
+  }
+
   //
   // ASSERT both strings are less long than PcdMaximumAsciiStringLength
   //