diff --git a/adb/adb_commands.py b/adb/adb_commands.py
index f3667c8..bdf315b 100644
--- a/adb/adb_commands.py
+++ b/adb/adb_commands.py
@@ -297,7 +297,7 @@ def Pull(self, device_filename, dest_file=None, timeout_ms=None, progress_callba
             dest_file = io.BytesIO()
         elif isinstance(dest_file, str):
             dest_file = open(dest_file, 'wb')
-        elif isinstance(dest_file, file):
+        elif hasattr(dest_file, 'write'):
             pass
         else:
             raise ValueError("destfile is of unknown type")
diff --git a/adb/filesync_protocol.py b/adb/filesync_protocol.py
index d0547f4..3b36af3 100644
--- a/adb/filesync_protocol.py
+++ b/adb/filesync_protocol.py
@@ -139,7 +139,7 @@ def Push(cls, connection, datafile, filename,
         cnxn.Send(b'SEND', fileinfo)
 
         if progress_callback:
-            total_bytes = os.fstat(datafile.fileno()).st_size if isinstance(datafile, file) else -1
+            total_bytes = os.fstat(datafile.fileno()).st_size if hasattr(datafile, 'fileno') else -1
             progress = cls._HandleProgress(lambda current: progress_callback(filename, current, total_bytes))
             next(progress)