diff --git a/MdePkg/Library/BaseLib/HighBitSet32.c b/MdePkg/Library/BaseLib/HighBitSet32.c
index 65f067ac1a..5ab4d7fe8d 100644
--- a/MdePkg/Library/BaseLib/HighBitSet32.c
+++ b/MdePkg/Library/BaseLib/HighBitSet32.c
@@ -36,6 +36,9 @@ HighBitSet32 (
 {
   INTN                              BitIndex;
 
-  for (BitIndex = -1; Operand != 0; BitIndex++, Operand >>= 1);
+  if (Operand == 0) {
+    return - 1;
+  }
+  for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
   return BitIndex;
 }
diff --git a/MdePkg/Library/BaseLib/HighBitSet64.c b/MdePkg/Library/BaseLib/HighBitSet64.c
index 50889777b5..6b3c585f37 100644
--- a/MdePkg/Library/BaseLib/HighBitSet64.c
+++ b/MdePkg/Library/BaseLib/HighBitSet64.c
@@ -34,10 +34,19 @@ HighBitSet64 (
   IN      UINT64                    Operand
   )
 {
-  INTN                              BitIndex;
+  if (Operand == (UINT32)Operand) {
+    //
+    // Operand is just a 32-bit integer
+    //
+    return HighBitSet32 ((UINT32)Operand);
+  }
 
-  for (BitIndex = -1;
-       Operand != 0;
-       BitIndex++, Operand = RShiftU64 (Operand, 1));
-  return BitIndex;
+  //
+  // Operand is really a 64-bit integer
+  //
+  if (sizeof (UINTN) == sizeof (UINT32)) {
+    return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
+  } else {
+    return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
+  }
 }