diff --git a/BaseTools/Source/Python/GenFds/Fv.py b/BaseTools/Source/Python/GenFds/Fv.py
index ef5896d76b..0fb2bd456a 100644
--- a/BaseTools/Source/Python/GenFds/Fv.py
+++ b/BaseTools/Source/Python/GenFds/Fv.py
@@ -316,7 +316,7 @@ class FV (FvClassObject):
                                           ' %s' %ErasePloarity    + \
                                           T_CHAR_LF)
         if not (self.FvAttributeDict is None):
-            for FvAttribute in self.FvAttributeDict:
+            for FvAttribute in self.FvAttributeDict.keys() :
                 if FvAttribute == "FvUsedSizeEnable":
                     if self.FvAttributeDict[FvAttribute].upper() in ('TRUE', '1') :
                         self.UsedSizeEnable = True