diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index ac1e78002..dd364eedc 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -2057,7 +2057,8 @@ def sanitize_open(filename, open_mode):
                 import msvcrt
                 msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
             return (sys.stdout.buffer if hasattr(sys.stdout, 'buffer') else sys.stdout, filename)
-        stream = open(encodeFilename(filename), open_mode)
+        stream = locked_file(encodeFilename(filename), open_mode, block=False)
+        stream = stream.__enter__()
         return (stream, filename)
     except (IOError, OSError) as err:
         if err.errno in (errno.EACCES,):
@@ -2069,7 +2070,8 @@ def sanitize_open(filename, open_mode):
             raise
         else:
             # An exception here should be caught in the caller
-            stream = open(encodeFilename(alt_filename), open_mode)
+            stream = locked_file(encodeFilename(filename), open_mode, block=False)
+            stream = stream.__enter__()
             return (stream, alt_filename)
 
 
@@ -3498,15 +3500,18 @@ else:
     try:
         import fcntl
 
-        def _lock_file(f, exclusive):
-            fcntl.flock(f, fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH)
+        def _lock_file(f, exclusive, block):
+            if block:
+                fcntl.flock(f, fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH)
+            else:
+                fcntl.flock(f, fcntl.LOCK_EX|fcntl.LOCK_NB if exclusive else fcntl.LOCK_SH)
 
         def _unlock_file(f):
             fcntl.flock(f, fcntl.LOCK_UN)
     except ImportError:
         UNSUPPORTED_MSG = 'file locking is not supported on this platform'
 
-        def _lock_file(f, exclusive):
+        def _lock_file(f, exclusive, block):
             raise IOError(UNSUPPORTED_MSG)
 
         def _unlock_file(f):
@@ -3514,15 +3519,16 @@ else:
 
 
 class locked_file(object):
-    def __init__(self, filename, mode, encoding=None):
-        assert mode in ['r', 'a', 'w']
+    def __init__(self, filename, mode, block=True, encoding=None):
+        assert mode in ['r', 'rb', 'a', 'ab', 'w', 'wb']
         self.f = io.open(filename, mode, encoding=encoding)
         self.mode = mode
+        self.block = block
 
     def __enter__(self):
-        exclusive = self.mode != 'r'
+        exclusive = self.mode not in ['r', 'rb']
         try:
-            _lock_file(self.f, exclusive)
+            _lock_file(self.f, exclusive, self.block)
         except IOError:
             self.f.close()
             raise
@@ -3543,6 +3549,11 @@ class locked_file(object):
     def read(self, *args):
         return self.f.read(*args)
 
+    def flush(self, *args):
+        self.f.flush()
+
+    def close(self, *args):
+        self.__exit__(self, *args, value=False, traceback=False)
 
 def get_filesystem_encoding():
     encoding = sys.getfilesystemencoding()