2to3 --fix=dict with manual cleanup
diff --git a/Lib/fontTools/ttLib/sfnt.py b/Lib/fontTools/ttLib/sfnt.py
index d69b7b7..3cac90f 100644
--- a/Lib/fontTools/ttLib/sfnt.py
+++ b/Lib/fontTools/ttLib/sfnt.py
@@ -238,7 +238,7 @@
 
 	def _calcMasterChecksum(self, directory):
 		# calculate checkSumAdjustment
-		tags = self.tables.keys()
+		tags = list(self.tables.keys())
 		checksums = []
 		for i in range(len(tags)):
 			checksums.append(self.tables[tags[i]].checkSum)