diff --git a/pdbfixer/pdbfixer.py b/pdbfixer/pdbfixer.py
index 766d50f..fc8d715 100644
--- a/pdbfixer/pdbfixer.py
+++ b/pdbfixer/pdbfixer.py
@@ -242,7 +242,7 @@ def __init__(self, filename=None, pdbfile=None, pdbxfile=None, url=None, pdbid=N
             self.source = filename
             file = open(filename, 'r')
             if _guessFileFormat(file, filename) == 'pdbx':
-                self._initializeFromPDBx(file.read())
+                self._initializeFromPDBx(file)
             else:
                 self._initializeFromPDB(file)
             file.close()