diff --git a/stdlib/3/io.pyi b/stdlib/3/io.pyi
index ab32adc5f..351d5be86 100644
--- a/stdlib/3/io.pyi
+++ b/stdlib/3/io.pyi
@@ -206,4 +206,6 @@ class StringIO(TextIOWrapper):
     def __enter__(self) -> StringIO: ...
 
 class IncrementalNewlineDecoder(codecs.IncrementalDecoder):
+    def __init__(self, decoder: Optional[codecs.IncrementalDecoder],
+                 translate: bool, errors: str = ...) -> None: ...
     def decode(self, input: Union[bytes, str], final: bool = ...) -> str: ...