diff --git a/mitmproxy/net/websockets/frame.py b/mitmproxy/net/websockets/frame.py
index ac6a08128..7b93bc245 100644
--- a/mitmproxy/net/websockets/frame.py
+++ b/mitmproxy/net/websockets/frame.py
@@ -71,7 +71,7 @@ class FrameHeader:
         else:
             self.length_code = length_code
 
-        if mask is DEFAULT and masking_key is DEFAULT:
+        if (mask is DEFAULT and masking_key is DEFAULT) or mask == 0 or mask is False:
             self.mask = False
             self.masking_key = b""
         elif mask is DEFAULT:
diff --git a/test/mitmproxy/net/websockets/test_frame.py b/test/mitmproxy/net/websockets/test_frame.py
index 2a5bd5561..f5c29c21b 100644
--- a/test/mitmproxy/net/websockets/test_frame.py
+++ b/test/mitmproxy/net/websockets/test_frame.py
@@ -122,7 +122,7 @@ class TestFrameHeader:
 
         f = websockets.FrameHeader(masking_key=b"foob", mask=0)
         assert not f.mask
-        assert f.masking_key
+        assert not f.masking_key
 
 
 class TestFrame:
diff --git a/test/pathod/language/test_websockets.py b/test/pathod/language/test_websockets.py
index ed766bca6..64ff024c9 100644
--- a/test/pathod/language/test_websockets.py
+++ b/test/pathod/language/test_websockets.py
@@ -123,12 +123,6 @@ class TestWebsocketFrame:
         assert not frm.header.mask
         assert not frm.header.masking_key
 
-        frm = self.fr("wf:b'foo':-mask:k'abcd'", is_client=True)
-        assert not frm.header.mask
-        # We're reading back a corrupted frame - the first 3 characters of the
-        # mask is mis-interpreted as the payload
-        assert frm.payload == b"abc"
-
     def test_knone(self):
         with pytest.raises(Exception, match="Expected 4 bytes"):
             self.fr("wf:b'foo':mask:knone")