diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index de602380..c6e57dba 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,6 +7,11 @@ Changelog
 .. This document is user facing. Please word the changes in such a way
 .. that users understand how the changes affect the new version.
 
+version 1.6.0-dev
+-----------------
++ Fix an error that occurred in the ``__close__`` function when a threaded
+  writer was initialized with incorrect parameters.
+
 version 1.5.3
 -----------------
 + Fix a bug where append mode would not work when using
diff --git a/src/isal/igzip_threaded.py b/src/isal/igzip_threaded.py
index 99eafc17..adb2c24d 100644
--- a/src/isal/igzip_threaded.py
+++ b/src/isal/igzip_threaded.py
@@ -204,6 +204,9 @@ def __init__(self,
                  queue_size: int = 1,
                  block_size: int = 1024 * 1024,
                  ):
+        # File should be closed during init, so __exit__ method does not
+        # touch the self.raw value before it is initialized.
+        self._closed = True
         if "t" in mode or "r" in mode:
             raise ValueError("Only binary writing is supported")
         if "b" not in mode:
@@ -243,8 +246,8 @@ def __init__(self,
         self._crc = 0
         self.running = False
         self._size = 0
-        self._closed = False
         self.raw = open_as_binary_stream(filename, mode)
+        self._closed = False
         self._write_gzip_header()
         self.start()