diff --git a/BaseTools/Source/C/VfrCompile/Pccts/h/DLexer.h b/BaseTools/Source/C/VfrCompile/Pccts/h/DLexer.h
index 37cac24f14..f15bff1187 100644
--- a/BaseTools/Source/C/VfrCompile/Pccts/h/DLexer.h
+++ b/BaseTools/Source/C/VfrCompile/Pccts/h/DLexer.h
@@ -30,6 +30,8 @@
  * 1989-2000
  */
 
+#include <assert.h>
+
 #define ZZINC {if ( track_columns ) (++_endcol);}
 
 #define ZZGETC {ch = input->nextChar(); cl = ZZSHIFT(ch);}
@@ -114,6 +116,7 @@ more:
 		state = dfa_base[automaton];
 		while (ZZNEWSTATE != DfaStates) {
 			state = newstate;
+            assert(state <= sizeof(dfa)/sizeof(dfa[0]));
 			ZZCOPY;
 			ZZGETC;
 			ZZINC;
diff --git a/BaseTools/Source/C/VfrCompile/VfrUtilityLib.cpp b/BaseTools/Source/C/VfrCompile/VfrUtilityLib.cpp
index 1ab95bec0a..24b0bfa6fd 100644
--- a/BaseTools/Source/C/VfrCompile/VfrUtilityLib.cpp
+++ b/BaseTools/Source/C/VfrCompile/VfrUtilityLib.cpp
@@ -1474,6 +1474,10 @@ CVfrDataStorage::GetFreeVarStoreId (
     }
   }
 
+  if (Index == EFI_FREE_VARSTORE_ID_BITMAP_SIZE) {
+    return EFI_VARSTORE_ID_INVALID;
+  }
+
   for (Offset = 0, Mask = 0x80000000; Mask != 0; Mask >>= 1, Offset++) {
     if ((mFreeVarStoreIdBitMap[Index] & Mask) == 0) {
       mFreeVarStoreIdBitMap[Index] |= Mask;
@@ -2437,6 +2441,10 @@ CVfrQuestionDB::GetFreeQuestionId (
     }
   }
 
+  if (Index == EFI_FREE_QUESTION_ID_BITMAP_SIZE) {
+    return EFI_QUESTION_ID_INVALID;
+  }
+
   for (Offset = 0, Mask = 0x80000000; Mask != 0; Mask >>= 1, Offset++) {
     if ((mFreeQIdBitMap[Index] & Mask) == 0) {
       mFreeQIdBitMap[Index] |= Mask;