diff --git a/MySQLdb/MySQLdb/cursors.py b/MySQLdb/MySQLdb/cursors.py
index 7bd1d55..4cdabf9 100644
--- a/MySQLdb/MySQLdb/cursors.py
+++ b/MySQLdb/MySQLdb/cursors.py
@@ -231,7 +231,7 @@ class CursorStoreResultMixIn:
         """Fetch up to size rows from the cursor. Result set may be smaller
         than size. If size is not defined, cursor.arraysize is used."""
         self._check_executed()
-        end = self.rownumber + size or self.arraysize
+        end = self.rownumber + (size or self.arraysize)
         result = self._rows[self.rownumber:end]
         self.rownumber = min(end, len(self._rows))
         return result