diff --git a/xlsx2csv.py b/xlsx2csv.py
index 37f5deb..5bcd376 100755
--- a/xlsx2csv.py
+++ b/xlsx2csv.py
@@ -528,7 +528,7 @@ def parse(self, filehandle):
                 if cellXfs._attrs and 'numFmtId' in cellXfs._attrs:
                     numFmtId = int(cellXfs._attrs['numFmtId'].value)
                     if self.chk_exists(numFmtId) == None:
-                        numFmtId = int(cellXfs._attrs['applyNumberFormat'].value)
+                        numFmtId = int(cellXfs._attrs['applyNumberFormat'].value == 'true')
                     self.cellXfs.append(numFmtId)
                 else:
                     self.cellXfs.append(None)