diff --git a/tests/extmod/uzlib_decompio.py b/tests/extmod/uzlib_decompio.py
index ee3204d07..75a6df0ca 100644
--- a/tests/extmod/uzlib_decompio.py
+++ b/tests/extmod/uzlib_decompio.py
@@ -7,7 +7,7 @@ import uio as io
 
 # Raw DEFLATE bitstream
 buf = io.BytesIO(b'\xcbH\xcd\xc9\xc9\x07\x00')
-inp = zlib.DecompIO(buf)
+inp = zlib.DecompIO(buf, -8)
 print(buf.seek(0, 1))
 print(inp.read(1))
 print(buf.seek(0, 1))
@@ -17,3 +17,16 @@ print(buf.seek(0, 1))
 print(inp.read(1))
 print(inp.read())
 print(buf.seek(0, 1))
+
+
+# zlib bitstream
+inp = zlib.DecompIO(io.BytesIO(b'x\x9c30\xa0=\x00\x00\xb3q\x12\xc1'))
+print(inp.read(10))
+print(inp.read())
+
+# zlib bitstream, wrong checksum
+inp = zlib.DecompIO(io.BytesIO(b'x\x9c30\xa0=\x00\x00\xb3q\x12\xc0'))
+try:
+    print(inp.read())
+except OSError as e:
+    print(repr(e))
diff --git a/tests/extmod/uzlib_decompio.py.exp b/tests/extmod/uzlib_decompio.py.exp
index 6ef811d7d..3f5f360fa 100644
--- a/tests/extmod/uzlib_decompio.py.exp
+++ b/tests/extmod/uzlib_decompio.py.exp
@@ -7,3 +7,6 @@ b'lo'
 b''
 b''
 7
+b'0000000000'
+b'000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
+OSError(22,)